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Elmcare.com - All about elm trees and elm tree care. Home | Elm Care Products | Register your Elm | Forum Last Update 17/12/01 How Trees Work About Elm Trees Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts Visit TreeHelp.com for all of your tree and shrub care needs Customized Elm Tree Care Kits Custom care kits include specialized and innovative soil treatments designed to promote root development and the long- term health and vitality of your elm. A healthier elm will be better able to fight against Dutch elm disease. more Elm Tree Registry Register your elm tree to receive customized care advice... more. Return of the Stately Elm Writer and broadcaster Jamie Swift examines the Canadian city of Winnipeg's struggle to combat Dutch elm disease. Through the work of community groups like the Coalition to Save the Elms and innovative technology, the city has achieved substantial success... more. Did you know a new wild bird seed has been developed and tested that actually repels squirrels? Click here to learn about Squirrel Proof Wild Bird Seed. http://www.elmcare.com/index.htm (1 of 2) [2/27/02 10:29:57 PM]
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Page 1: Home Elm Care Products Register your Elm Forum · Elmcare.com - All about elm trees and elm tree care. Home | Elm Care Products | Register your Elm | Forum Last Update 17/12/01 How

Elmcare.com - All about elm trees and elm tree care.

Home | Elm Care Products | Register your Elm | Forum

Last Update 17/12/01

How Trees Work

About Elm Trees

Caring for Your Elm

Elm Tree Diseases

Elm Tree Links

Quick Elm Facts

Visit TreeHelp.com for all of your tree and shrub care needs

Customized Elm Tree Care Kits

Custom care kits include specialized and innovative soil treatments designed to promote root development and the long-term health and vitality of your elm. A healthier elm will be better able to fight against Dutch elm disease.more

Elm Tree Registry

Register your elm tree to receive customized care advice...more.

Return of the Stately Elm

Writer and broadcaster Jamie Swift examines the Canadian city of Winnipeg's struggle to combat Dutch elm disease. Through the work of community groups like the Coalition to Save the Elms and innovative technology, the city has achieved substantial success... more.

Did you know a new wild

bird seed has been developed and tested that actually repels squirrels? Click here to learn about Squirrel Proof Wild Bird

Seed.

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Page 2: Home Elm Care Products Register your Elm Forum · Elmcare.com - All about elm trees and elm tree care. Home | Elm Care Products | Register your Elm | Forum Last Update 17/12/01 How

Elmcare.com - All about elm trees and elm tree care.

New Treatments for Dutch Elm Disease?

Researchers examine new ways to fight this devastating disease.

Elm Species

Elms come in many sizes and shapes...learn about them all.

Elms in History

Look at elms in the context of human history.

Elms in Literature

Read what some of the world's leading poets and authors have written of the elm.

Elm Tree Links

Links to a growing community of academics, homeowners and professional tree care experts.

Quick Elm Facts

Discover something new and interesting about the elm.

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Page 3: Home Elm Care Products Register your Elm Forum · Elmcare.com - All about elm trees and elm tree care. Home | Elm Care Products | Register your Elm | Forum Last Update 17/12/01 How

How Trees Work

Home | Elm Care Products | Register your Elm | Forum

Home > How Trees Work Last Update 30/08/00

How Trees Work

Types of TreesImportant FactsStructure of a TreeHow Trees BreatheHow Trees Drink

About Elm Trees Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

What is a ring-porous vascular system? What is the difference between wild-type and cloned trees?

Find the answers to these questions and more by clicking on one of the topics below:

More Info... Important Facts Types of Trees Structure of a Tree How Trees Drink How Trees Breathe

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Page 4: Home Elm Care Products Register your Elm Forum · Elmcare.com - All about elm trees and elm tree care. Home | Elm Care Products | Register your Elm | Forum Last Update 17/12/01 How

Types of Trees

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How Trees Work

Types of Trees Important FactsStructure of a TreeHow Trees BreatheHow Trees Drink

About Elm Trees Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

Angiosperms vs. Gymnosperms

Trees are scientifically divided into two major categories: angiosperms and gymnosperms.

Angiosperms are flowering plants and their seeds are encased in a protective ovary. This division contains the larger number of species can be further subdivided into dicots and monocots. Dicots have two seed leaf structures and include many broadleaf trees such as the elm, maple and oak. Monocots have one seed leaf structure and include species such as the palm.

Gymnosperms, on the other hand, do not produce flowers. Their seeds have structures such as cones, rather than a protective ovary. Conifers (needle-leaf trees) are a major group of gymnosperms.

Deciduous vs. Coniferous

Trees can also be divided into deciduous and coniferous categories.

Deciduous trees are also known as broadleaf trees because the leaves are generally larger and wider than those of conifers. The larger leaf size means a greater surface area for photosynthesis, but it also mean the leaf is too fragile to withstand winter conditions. Therefore, most deciduous trees drop their leaves in autumn.

Coniferous trees keep their leaves throughout the year, shedding only the oldest leaves. Usually these leaves are lower down on the tree and do not receive as much sunlight as newly developed leaves higher up. Some of the best-known members of the conifer family are pines, spruces, firs, and hemlocks. The cones of the conifers are its flowers.

http://www.elmcare.com/trees/types_of_trees.htm (1 of 2) [2/27/02 10:30:04 PM]

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Types of Trees

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Page 6: Home Elm Care Products Register your Elm Forum · Elmcare.com - All about elm trees and elm tree care. Home | Elm Care Products | Register your Elm | Forum Last Update 17/12/01 How

Important Facts About Trees

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Home > How Trees Work > Important Facts Last Update 30/08/00

How Trees Work

Types of TreesImportant Facts Structure of a TreeHow Trees BreatheHow Trees Drink

About Elm Trees Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

Some trees are wild, others are cloned

It's easy to think that all trees of a species are alike. This is only true, however, of certain species. Most trees are wild-type trees, meaning that their genetic make-ups are as dissimilar as individual humans. An example of a wild-type is an elm.

Other trees have been cloned to produce many trees with identical genes. This is usually done to guarantee the presence of certain favourable characteristics of the tree. Examples include apple and pear trees.

This distinction is important when treating diseases. In a wild-type tree, each tree will react differently.

Some trees are ring-porous, some are diffuse-porous

Trees can be divided into ring-porous or diffuse-porous types. This refers to the structure of the vascular system.

The vascular system of diffuse-porous trees (such as a birch) is characterized by vessels spread evenly throughout the sapwood. These vessels are produced regularly during the growing season.

Diffuse-Porous

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Important Facts About Trees

The vessels of a ring-porous tree (such as an elm) are generally larger and concentrated in the outermost layer of sapwood. These vessels are produced early in the season.

Ring-Porous

This is significant because it affects a tree's susceptibility to vascular wilt diseases. Ring-porous vascular systems are very efficient, but are much more vulnerable to blockage. The elm's vulnerability to Dutch elm disease is an case in point.

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Page 8: Home Elm Care Products Register your Elm Forum · Elmcare.com - All about elm trees and elm tree care. Home | Elm Care Products | Register your Elm | Forum Last Update 17/12/01 How

Structures of Trees

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How Trees Work

Types of TreesImportant FactsStructure of a Tree How Trees BreatheHow Trees Drink

About Elm Trees Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

Leaves

The leaves convert carbon dioxide into oxygen and provide the tree with energy to grow and fight disease...more.

Roots

The roots provide structural stability to the tree and are the means by which it takes up water and minerals...more.

Bark

Bark is the outer protective covering of tree trunks. The form and structure of bark can differ greatly from tree to tree...more.

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How Trees Breathe

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How Trees Work

Types of TreesImportant FactsStructure of a TreeHow Trees Breathe How Trees Drink

About Elm Trees Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

Acting as an enormous "carbon sink", trees soak up carbon dioxide from the air, producing life-giving oxygen in return. In fact, a medium-sized tree generates the same amount of oxygen as each one of us needs to breathe.

In a tree, 'breathing' takes place in the leaf. Chlorophyll (the substance causing the green colour) absorbs the CO2 and uses it along with water to dissolve minerals taken up through the roots. After the chemical reaction is completed, the leaf releases oxygen and water vapor through its pores.

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How Trees Drink

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How Trees Work

Types of TreesImportant FactsStructure of a TreeHow Trees BreatheHow Trees Drink

About Elm Trees Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

There are two ways that a tree can take in water: through the leaves and through the roots.

Trees absorb small amounts of moisture from the air through their leaves and their bark. Most of their water, however, comes via the roots.

Water enters the roots through thin membranes at their tips. The tree's vascular system draws the water up through the trunk and distributes it to the leaves. The leaves use the water to dissolve minerals. Excess water goes back to the air through pores in the leaf - a process called transpiration.

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About Elm Trees

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How Trees Work

About Elm Trees

The Elm StoryIdentifying ElmsElm SpeciesBiology of Elms

Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

The majestic elm is one of the most beloved of all our trees.

Dutch elm disease has taken its toll and sadly the elm is disappearing from our landscape.

But through community action, new research and a concentrated effort, the elm can make a comeback.

Perhaps soon, the stately elm can reclaim its rightful place in our lives.

Click on one of the following to learn more.

More Info... The Elm Story Identifying Elms Elm Species Biology of Elms

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The Elm Story

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How Trees Work

About Elm Trees

The Elm Story Identifying ElmsElm SpeciesBiology of Elms

Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

The adjectives “majestic” and “stately” leap to mind when describing elms. These trees are truly one of our most recognizable trees whether lining our streets and boulevards or standing on guard in a farmer's field. The number of “Elm” streets, parks and buildings demonstrates just how much a part of our lives these trees became.

To learn more, click on one of the topics below:

More Info... The Cultivated Elm Elms in Literature Living History Elms in Mythology

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Identifying Elms

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How Trees Work

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The Elm StoryIdentifying Elms Elm SpeciesBiology of Elms

Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

Elm trees make up an important part of the North American landscape and identifying them is the first step in preventing their demise from Dutch elm disease. Although there are differences amongst the different species of elms, this section will focus on the American elm, which is the most widespread.

To quickly identify an elm, look at the silhouette, the leaves and the bark.

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Elmcare.com - Elm Species

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How Trees Work

About Elm Trees

The Elm StoryIdentifying ElmsElm Species Biology of Elms

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Click on one of the elm species below to discover more.

Common Name : Scientific Name American Elm : Ulmus americana L.

Rock Elm : Ulmus Thomasii Sarg. Slippery Elm : Ulmus rubra Muehl. Scotch Elm : Ulmus glabra Huds.

Camperdown Elm : Ulmus glabra camperdownii Siberian Elm : Ulmus pumila L. English Elm : Ulmus procera Salisb.

Japanese Zelkova : Zelkova serrata Thunb. Mak. Winged Elm : Ulmus alata

Chinese or Hokkaido Elm : Ulmus parvifolia

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Biology of Elms

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How Trees Work

About Elm Trees

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Caring for Your Elm Elm Tree Diseases Elm Tree Links Quick Elm Facts

40 Million Years OldElm trees first made an appearance in the Miocene period, about 40 million years ago.

Originating in central Asia, the tree has flourished and has established itself over most of North America, Europe and Asia.

Vascular Plants

Understanding how an elm tree lives and breathes is important in understanding how Dutch elm disease has spread.

Just like the human cardio-vascular system of arteries and veins, a tree has a vascular system of long thin vertical tubes. This vascular system takes the water and nutrients from the roots and distributes them throughout the tree.

In an elm, the cells that produce the vascular tubes are found just beneath the bark in a layer called the cambium. After each growing season, the inner part of the cambium dies. A new cambium is formed the next spring. If you cut through a tree trunk, you can see the tree rings. Each ring is a cambium layer.

An elm tree has a very efficient vascular system but that also makes it vulnerable. The same qualities that allow the elm to efficiently draw water to its upper leaves also give fungi and insects easy access to the inner workings of the tree. The fungus that causes Dutch elm disease, for example, essentially clogs the elm tree’s vascular system.

Dutch elm disease can be treated. However, because the tree’s vascular system is renewed every year, treatments have to be repeated annually.

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Elmcare.com - Caring for your Elm Tree

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Last Update 26/04/01

How Trees Work About Elm Trees

Caring for Your Elm Tree

FertilizingPruningLawn CareWateringObstaclesDisposal

Elm Tree Diseases Elm Tree Links Quick Elm Facts

Trees are a constant in our lives. They seem to last forever (they certainly outlive us) and their branches cast a protective shadow over generation after generation.

So strong and hardy are trees that we often assume that they endure just about any hardship without any help from us.

But trees outside their natural setting are often under tremendous stress.

And yes, there is much we can do to help them.

Fertilizing; pruning; giving the tree room to grow and breathe. We can help our trees to thrive and ensure that they can continue to give pleasure for generations to come.

Click on one of the following for more information:

Fertilizing Watering

Pruning Obstacles to Growth

Lawn Care Disposal of Dead Elms

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Elmcare.com - Fertilizing

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How Trees Work About Elm Trees

Caring for Your

Elm Tree

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Elm Tree Diseases Elm Tree Links Quick Elm Facts

Elms should be fertilized once or twice a year. However, not just any fertilizer will do and using the wrong type of fertilizer can actually increase the chances that your tree will contract Dutch elm disease. Avoid standard "one-size-fits-all" lawn and turf fertilizer. In particular, fertilizers that release large amounts of Nitrogen quickly into the soil can encourage structurally weak growth that could attract the elm bark beetles carrying the Dutch elm disease fungus. Aside from the formulation, the method of fertilization differs from that of your grass. In order to give your trees the most benefit, the fertilizer must be placed below the grass roots.

To find out how to obtain fertilizer specially selected for use on elm trees, click here.

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Elmcare.com - Pruning Elm Trees

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Pruning is one of the most important ways we can help our trees.

Regular removal of dead branches:

● decreases the breeding area for disease-carrying insects● promotes growth● removes safety hazards● improve the tree’s appearance.

Take care! Improper or untimely pruning can do more harm than good.

Click on a topic to learn more:

Why Prune? Timing

Types of Pruning Pruning Pitfalls

Technique

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Elmcare.com - Lawn Care

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Grass and trees are not always the best of friends.

In natural settings, the ground around large shade trees is covered with leaves. As the leaves decompose, they release nutrients which the tree needs. Not so in our cities where are trees are surrounded by grass. The grass actually competes with the tree for water and nutrients.

How you care for your lawn can affect the health of your elm tree.

Fertilizing Scatter fertilizer around a tree and you will end up with very healthy grass. Tree food stakes inserted into the ground release nutrients below the grass layer. Use fertilizers specifically designed for shade or elm trees.

Mowing Take care when mowing. Lawn mowers can damage a tree. Better yet, avoid the problem by keeping the grass back from the base of the tree. A buffer zone of loose soil or mulch is ideal.

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Elmcare.com - Watering Elm Trees

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Water is, of course, vital to the survival and health of a tree. You can provide a tree with the moisture it needs.

How

A tree takes moisture in through its root system. At the tip of the root, there are tiny structures called root hairs which absorb moisture from the surrounding soil. This is where you want to target your watering.

In an elm, the tips of the roots are usually located outside of the weeping or drip line. This is the outermost extent of the crown of the tree. Therefore, sprinkling water onto the trunk will have little or adverse effect on the tree's health.

It is important to remember that grass and other vegetation compete with a tree for moisture. As a result, sprinkling is not a very efficient method of watering. Firstly, there is extensive evaporation, and secondly the grass absorbs a large percentage of this water.

A preferable method of watering is to soak the ground outside the weeping line with a hose. There are also special devices that allow you to apply moisture directly into the ground near the roots.

It is important to allow the soil to dry in between waterings. If the soil is constantly wet, it can easily become compacted, hindering gas exchange with the air.

When

Often nature provides all the moisture a tree needs. It is times of drought or in certain urban environments when watering is required.

● Examine the leaves: wilting, browning, discoloured margins - these are all signs your tree needs moisture

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Elmcare.com - Watering Elm Trees

● Examine the grass: if your lawn is yellowing, there is good chance that your tree lacks moisture even if it has yet to show signs.

● Examine nearby trees: If other trees in your area show signs of drought, your tree may be next. Often other species, such as maples, show signs earlier than elms giving an early warning signal.

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Elmcare.com - Obstacles to Growth

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Sidewalks, utility lines, houses, poor soil, polluted air - it is a wonder that our trees do as well as they do. We can help our trees thrive and grow by managing some of the obstacles they face.

Physical Obstacles

Due to the sheer size of a mature elm, things tend to get in its way. The easiest way to avoid conflicts with physical obstacles is to plan around them. This means care when planting.

A young tree always looks lonely in a garden. But that spindly litle tree will eventually grow to be more than 30 metres tall with a crown that will engulf everything nearby. Elm trees should be planted at least 5 metres (15 feet) away from houses.

Never plant an American Elm under utility lines. The result will be frequent and costly pruning.

Construction

When doing construction around an elm tree, care must be taken to avoid cutting the root system.

It is difficult for the tree to close root wounds. Cutting roots can leave the tree vulnerable to attack by a fungal disease such as Dutch Elm Disease.

If cutting the root is unavoidable, attempt to make clean cuts exposing as little surface area as possible.

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Elmcare.com - Obstacles to Growth

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Elmcare.com - Disposal of Dead Elms

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A dead elm tree is a threat to all the other elm trees in the neighbourhood.

Because dead wood is an ideal breeding ground for the elm bark beetle and the DED fungus, disposal of dead limbs and trees must be done properly and quickly.

If you have a dead elm, first remove the major limbs and proceed to cut down the tree.Remember taking trees down is not a job for the amateur. Call a tree removal company. Some municipalities offer disposal services for large trees.

Wood should be burned immediately. It should not be stored. Some communities have strict by-laws prohibiting the storage and transportation of elm firewood.

If there is insufficient space for burning, the wood can be buried.

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Elmcare.com - Elm Tree Diseases

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While elm trees are extremely hardy, they are still susceptible to attack from diseases or insects.

If your elm tree seems unhealthy, it could be suffering from one of the diseases on the left.

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Elmcare.com - Dutch Elm Disease

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Dutch elm disease (DED) is the most devastating shade tree disease in North America. It is a wilt disease with an extremely high fatality rate among elms.

How Dutch Elm Disease KillsDutch elm disease (or DED) is caused by a fungus. After the disease is contracted, spores rapidly reproduce and spread toxins throughout the tree.

The fungus blocks the water-conducting or vascular system of the tree preventing water and minerals from reaching the branches and leaves. The leaves wilt and eventually the tree dies.

The FungusThe fungus Ophiostoma (Ceratocystis) ulmi attacks various species of elm. It can kill a tree within a few weeks or it can kill it gradually over a period of years.

There are two strains of the fungus in North America - the non-aggressive strain (O. ulmi) and the aggressive strain (O. novo-ulmi). While the elm’s natural defense mechanism tries to fight off the fungus, the aggressive strain often moves too quickly for the tree to react without human intervention.

How Long Does It Take for the Fungus to Destroy a Tree?That depends on the age and health of the tree. A younger fast-growing tree can die quickly. Some younger trees have some natural resistance to DED. However, this resistance tends to wear off after 15-20 years. Slow growing older trees can linger for a year or two.

Is There a Cure for DED?When an elm tree detects the presence of the fungus, it produces a number of defensive compounds. ‘Mansonones’, for example, are toxic to the DED fungus. However, left to its own devices, a tree cannot produce enough to fight off the disease.

Researchers are now learning how to stimulate the tree’s natural defenses to produce larger quantities of mansonones. It is a promising breakthrough. For more information on the new DED treatment, click here.

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Elmcare.com - Dutch Elm Disease

For more information on Dutch elm disease, click on one of the topics below:

History of Dutch elm disease Prevention of Dutch elm disease Transmission of Dutch elm disease Traditional Treatments Symptoms of Dutch elm disease Innovative Treatment

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History of Dutch Elm Disease

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Why “Dutch” elm disease?The Dutch may have been unfairly blamed for the loss of millions of trees. “Dutch” elm disease got its name because Dutch scientists identified it when the disease made an appearance in Holland in 1917. From there, it spread quickly wiping out many of the European elms.

Origins Scientists believe that the fungus that causes DED originally came from the Himalayas. It travelled to Europe from the Dutch East Indies in the late 1800’s. In the 1930’s, the disease spread to North America on wooden crates made with infected elm wood.

A second introduction of the disease in North America occurred in 1945 starting in Sorel, Quebec. It destroyed over half the remaining elm trees in eastern Canada and the US. By 1976, only 34 million elm trees were left.

New strains of the disease appeared in the 1960’s in England. Within 20 years, 17 million of the country’s 23 million elm trees were dead.

Moving West The disease has now spread to Manitoba and Saskatchewan where there are approximately 500,000 elm trees in the cities. Three to five percent of the elms die each year

Winnipeg is spending C$2.5 million a year on sanitation and pruning. Having lost 40,000 trees in the last 20 years, the city’s elm population is now just 200,000.

More Than Just Beauty Mature trees add to property values. The estimated value of a mature elm for insurance purposes is C$3,600 (US$2,500) per tree. With roughly 650,000 elms in cities in Canada, the elms are worth C$2.3 billion. The 7 million urban trees in the US are worth US$17.5 billion.

Source: "The American elm and Dutch elm disease" M. Hubbes, Forestry Chronicle, March/April

1999. Vol. 75, No. 2, p.265

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History of Dutch Elm Disease

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Transmission of Dutch Elm Disease

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Dutch elm disease can be transmitted from tree to tree by the elm bark beetle, root grafts and infected tools.

Elm Bark Beetle

The elm bark beetle (not to be confused with the Elm Leaf Beetle) is by far the most important factor in Dutch Elm Disease.

These tiny insects’ lives revolve around elm trees. The female beetle tunnels into the tree between the bark and the wood and lays its eggs. When the eggs hatch, the larvae tunnel further into the tree in order to feed before emerging as mature beetles.

Adults feed in the crown of the tree, moving from tree to tree before breeding again.

If a beetle breeds or feeds in a DED-infected tree, the sticky spores of the fungus become attached to its back. When the beetle moves to a healthy tree, so too do the spores.

There are two species of the elm bark beetle in North America – the European and the Native elm bark beetles. The European is more temperature sensitive and lives mainly in southern regions. The Native is dominant in the mid-west.

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Transmission of Dutch Elm Disease

Brood Gallery of Native Bark Beetle Brood Gallery of European Bark Beetle

The native elm bark beetle consists of two separate breeding groups. One group overwinters as larvae in the breeding tunnels, while the second group overwinters as adults. These adults emerge from mid-April to mid-May. It is their feeding phase that causes the majority of DED infections. It is believed that the European elm bark beetle overwinters as larvae.

Much of the effort to control the spread of DED has focused on controlling the beetle population with insecticides or trapping. These methods have enjoyed some degree of success but the beetles remain the single most important factor in the spread of the disease.

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Root Grafts

Mature elms have a large system of roots. When these roots come into contact with those of another elm, they can graft together to promote the exchange of nutrients. The fungus can spread through the root grafts, infecting the neighbouring trees.

A tree infected by root graft transmission shows very sudden and devastating symptoms. Treatment is much less effective.

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Infected Tools

Pruning tools can also transmit Dutch elm disease. All tools should be cleaned

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Transmission of Dutch Elm Disease

before pruning a healthy tree. Some arborists recommend a 10% solution of household bleach.

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Symptoms of Dutch Elm Disease

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An infected elm tree usually exhibits symptoms soon after infection. Because of the speed with which the disease attacks, detecting symptoms as early as possible is essential for treatment.

The first sign of the disease is the sudden wilting of leaves in the upper reaches of the tree

Next, the leaves change colour from green to yellow to brown. They then shrivel and die.

Timing

If the infection occurs very late in the season, the leaves will appear to fall normally. However, the following spring the new leaves will be smaller than normal. The tree will often die before mid-summer.

In late summer, it may be difficult to distinguish between wilting and natural fall colours.

Bark Signs

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Symptoms of Dutch Elm Disease

Discolouration of the wood is also a sign of the disease. If you peel back the bark on a wilted branch, you will see some streaking on the wood.

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Prevention of Dutch Elm Disease

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Integrated Sanitation Program

Traditionally, people have tried to control Dutch Elm Disease by stopping it from spreading. Many communities, like the City of Winnipeg, have adopted a highly co-ordinated program to try to save their elms.

SurveillanceDetection is the first step. The earlier the disease can be caught, the quicker it can be stopped. Some communities and government agencies have designated experts to help make a definitive diagnosis. Contact these experts at the first suspicion of DED. Early detection can help prevent infection of nearby trees.

DisposalDead wood is an ideal breeding ground for the elm bark beetle. Dead wood must be properly removed and destroyed.

Firewood spreads the disease. Storing elm firewood is illegal in many jurisdictions with active DED control programs.

All elm wood should be buried, burned or chipped immediately.

PruningPruning promotes tree health. Regular pruning helps a tree use its natural defenses against DED. It also removes breeding sites for the elm bark beetle. Click here for proper maintenance pruning techniques.

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Prevention of Dutch Elm Disease

An elm in downtown Toronto is pruned in winter to discourage further spread of DED

When you prune is as important as how you prune. Pruning creates open cuts in a tree’s bark that take time to heal. Since the elm bark beetle is attracted to these wounds, pruning should not take place from early April to late July when the beetle is active.

Some municipalities have by-laws stating when pruning can be legally done.

InsecticidesChemical insecticides are used to control the elm bark beetle.

Chemicals are sprayed on the crown, bark and base of the tree in early April when the beetles become active. The chemicals kill the emerging adult beetles before they can introduce the fungus by feeding on the tree. Insecticides include Methoxychlor, carbaryl (Sevin) and chlorpyrifos (Dursban).

Some cities spray all boulevard and park elms. They may also offer their services to individual homeowners.

Before using any chemicals, consult a professional arborist. Most insecticides can be harmful to people, pets and the environment.

Insecticides are used less than they were in the past because proper dead wood disposal is more effective.

FungicidesFungicides can help guard against Dutch elm disease.

Chemicals such as Arbotect 20-s, Alamo, and Lignasan, are injected into the tree through holes drilled in the base or in the root-flares.

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Prevention of Dutch Elm Disease

Fungicide injection is both a preventative measure and a treatment for infected elms. However, fungicide injections are best left to professional arborists. Preventative injections can actually have an adverse affect on a tree’s health making it more susceptible to DED infection.

Fungicide injection should never be used as a substitute for pruning and other measures.

Natural Resistance A team from the University of Toronto has recently developed an innovative approach to preventing Dutch elm disease.

An “elicitor” inserted into the tree stimulates the tree’s natural defense mechanism which in turn prevents the fungus from gaining a foothold in the tree’s vascular system.

For long term protection, the elicitor must be applied on an annual basis. Along with regular pruning, it is an extremely effective method to prevent DED. It is also completely safe because it uses the tree’s natural defenses.

For more information about the elicitor, click here.

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Traditional Treatments of Dutch Elm Disease

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PruningPruning is an extremely effective way to treat a tree infected with DED.

Timely removal of diseased wood checks the spread of the disease. It is however less effective for well-established infections or for root-graft infections.

When you prune is extremely important. Pruning opens fresh wounds in the tree that take time to heal. The elm bark beetles are attracted to these wounds.

Pruning should not take place while the beetles are active (from early April to late July). Some municipalities have by-laws defining when you are legally permitted to prune elm trees.

Technique

● On an infected tree, locate the wilted branch and remove the bark until sapwood can be found with no discoloration.

● Cut the branch approximately 10 feet below the discolored area. The farther below the discolored area the limb is cut, the greater the chance of freeing the elm of the disease.

● Properly dispose of dead wood.● Disinfect tools using a 10% household bleach solution.

The loss of a major limb is regrettable but it can prevent the loss of the tree. One study reported that 60% of the trees that had been pruned at the early signs of the disease survived.

If the symptoms are allowed to continue, however, the success rate plummets. Studies have shown that if less than 5% of a tree is infected, pruning successful stops the disease 65% of the time. If 20% of the tree is infected, the success rate drops to 0%. 1

Chemical FungicidesTreating elm trees with systemic fungicides is a popular way to combat the effects of Dutch elm disease. Chemicals are injected into the tree either through holes drilled in the base of the tree or in the root-flares. Some chemicals that are currently used include Arbotect 20-s, Alamo and Lignasan.

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Traditional Treatments of Dutch Elm Disease

Chemical fungicides can be effective for trees in the early stages of the disease. If, however, a tree has advanced DED or has contracted the disease through a root graft, fungicides have little or no effect.

Fungicides are not a substitute for pruning and other measures.

Due to the difficulty of the procedure, fungicide injections are best left to professional arborists. A preventative injection into a healthy tree can adversely affect its health making it more susceptible to a DED infection.

1 (Himlick and Ceplecha, 1976)

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Innovative Treatment for Dutch Elm Disease

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Jump ahead to:

Unique DiscoveryHow It Is Applied

How It WorksUsing ELMguard

The elicitor in pellet form being inserted into a young elm.

Over the past twenty years, a team of scientists from the University of Toronto, Faculty of Forestry, under the leadership of Dr. Martin Hubbes, has been working on an exciting, new all-natural treatment for the prevention of Dutch elm disease. The new treatment or "elicitor" does not work directly on the fungus causing Dutch elm disease. Instead, it stimulates the tree's own immune system. The treatment has a strong protective effect because it activates the tree's natural defense response to Dutch elm disease.

Unique Discovery

The treatment is based on a special natural protein which was discovered by the University of Toronto scientific team as a result of intensive advanced molecular biology research. The protein elicits a defensive response in the tree which enables it to resist the onset of the aggressive and deadly strain of Dutch elm disease. The treatment is unique because it is all natural - it contains no synthetic chemicals and is non-toxic.

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Innovative Treatment for Dutch Elm Disease

How It Is Applied

ELMguard is an annual treatment applied to the tree in the spring. It is injected directly into the tree in either a liquid or pellet form through small holes drilled in the tree's outer growth ring. After injecting ELMguard, a wax sealer is used to close the small holes. During the season, the tree then closes the hole naturally with new wood growth.

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How It Works

After the injection, the tree's vascular system absorbs the protein starting a series of defensive reactions.

These reactions include the production of mansonones and cell lignification (hardening). Mansonones are a naturally produced substance and play an important role in an elm tree's defense response against Dutch elm and other diseases.

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Using ELMguard

ELMguard should be used as part of a comprehensive elm care program which promotes good health, proper sanitation (pruning) and the use of the elicitor to boost the tree's immune response system.

ELMguard does not provide 100% protection against Dutch elm disease in all elm trees because of the simple fact that each elm is different. Just as each of us is genetically different from everyone else, the same is true for wild elms. Therefore, each tree will react slightly differently to the treatment. Also, general health of an individual tree is a major factor in determining ELMguard's effectiveness.

For further information on ELMguard and other natural treatments for the control and prevention of Dutch elm disease, visit www.elmguard.com.

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Innovative Treatment for Dutch Elm Disease

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Elmcare.com - Elm Leaf Beetle

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The elm leaf beetle is a pest which poses some danger to the elm tree.

Adult beetles are approximately ¼ inch long. Their colour fades from yellow to olive as they mature. They have black stripes on the wing covers and four black spots on the thorax. The larvae are about 1/2 inch long and a dull yellow colour.

The adults lay eggs on the underside of elm leaves in late May and early June. After they hatch, the larvae begin feeding on the flesh of the leaf, leaving only the veins intact. About three weeks later, the adults emerge and chew

small holes in the leaves.

A tree can survive an infestation of elm leaf beetles. However, its weakened state will make it more susceptible to other diseases such as Dutch elm disease.

Birds, toads and other insects are natural enemies of the elm leaf beetle. There are also a number of effective pesticides.

As many chemical pesticides can be poisonous, care should be taken to read the label before use.

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Elmcare.com - Verticillium Wilt

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Verticillium wilt is caused by a fungus that lives in the soil. The fungus penetrates the root system of susceptible plants, eventually blocking the plant’s water-conducting system.

The fungus affects more than 300 types of plants throughout the world - from raspberries and tomatoes, to maples and elms. Although the disease occurs in naturally forested areas, it is found mostly in landscape plantings.

How It Spreads

The two fungal species, V. alboatrum and V. dahliae, can survive in the soil for decades lying in wait for new plants to move in. The fungus usually enters the roots through wounds, but if the tree is weak, it can actually penetrate the root.

When a plant dies, the fungus enters a resting state, producing structures called “microsclerotia”. These structures can be easily transported from place to place when trees are transplanted. In dry conditions, these microsclerotia can by carried by the wind to infect new areas.

Tools can also carry the fungus, so proper sanitation procedures should be followed.

How the Fungus Kills

Once inside the root, the fungus reproduces and spreads through the tree via the xylem, or water-conducting tissue. As it spreads, it causes tissue damage and clogs the xylem, preventing water from reaching the outer branches. Without moisture and necessary nutrients, these outer limbs wilt and die.

Symptoms

The first sign of disease is a slight yellowing of the foliage (similar to symptoms of

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Dutch elm disease although with less extensive crown involvement). There is also discolouration of the wood. Branches, stems and roots show a light to dark brown staining of the sapwood. Cankers may form on the branch and stem.

Trees with extensive infection show reduced growth rates and branch dieback. Younger trees usually succumb within one year. Older trees tend to deteriorate for a few years before finally dying.

Control

Fertilizing

Fertilizing with a balanced mixture light on nitrogen (5-10-10) may help to alleviate some of the symptoms. High nitrogen fertilizers, however, should be avoided. They promote new growth that would be vulnerable to the fungus.

Natural Defenses

One area that does offer hope comes from the Forestry Department of the University of Toronto. A team led by Dr. Martin Hubbes has isolated a glycoprotein that can potentially boost the natural defenses of a tree. Although research so far has focused on Dutch elm disease, stimulation of natural defenses could also be effective with Verticillium wilt.

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Also known as Elm Phloem Necrosis, this disease infects trees native to North America, while European and Asian elms seem to be immune.

The first symptom is the death of root hairs and tips followed by foliar wilt. Leaves will turn yellow, then brown and curl up. Generally the tree dies a few weeks after foliar symptoms manifest themselves. Other symptoms include yellowing of the sapwood and a wintergreen odour emanating form the bark. The causal agent of elm yellows is a “mycoplasma-like organism” (MLO) which is classified between a virus and a bacterium. This organism is carried from tree to tree by leafhoppers. There is no known effective treatment for elm yellows, so disposal of infected trees is the only option. The most effective preventative measure is controlling the leafhopper population.

In order to do this, a homeowner can utilize a pesticide such as methoxychlor emulsifiable concentrate. Applied during the bud breaks, this chemical represents an effective control of the leafhopper. As most chemical pesticides are poisonous, care should be taken to read the label before use.

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Cankers are a fungal disease.

The leaves turn bright yellow (similar to the symptoms of Dutch elm disease) with reddish-brown to black cankers on the twigs and small branches. The infected leaves can stay on the tree for several weeks.

There is no chemical treatment. Pruning is the best way to manage this disease.

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Wetwood is caused by a bacterial infection and is very common in elms and many other species. The infection causes moisture to be retained in the wood and also produces metabolic gases that increase the internal pressures in the tree. Periodically the liquid will be forced out of the tree through wound sites. The liquid oozes out and down the tree, where other organisms colonize it. This liquid is called slime flux and is known to have a foul odour.

Wetwood becomes a problem only when enough infection sites occur on the tree to compromise its structural integrity. A professional or consulting arborist should judge this. Otherwise, wetwood can be viewed as somewhat beneficial, as the moist environment that it creates in the tree helps to prevent decay fungi from colonizing the tree. Symptoms appear as long discoloured streaks on the trunk. Leaves may also exhibit some scorch if the infection is extensive.

At present, there is no treatment for wetwood.

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Elm Leaf Black Spot, also called elm anthracnose, is another fungal disease affecting the leaves of an elm tree.

First, yellow spots appear on the topside of the leaves. These spots are followed by slightly raised black fruiting bodies.

Removing diseased leaves can aid in treatment.

Nurseries use chemicals such as Bordeaux and mancozeb but these are not recommended for home use.

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The elm leaf miner is a common pest throughout eastern North America.

This insect feeds inside the leaf. The larvae tunnel through the leaf forming blotches and discolouration. As the miners move to the outer edge of the leaf, the leaf turns brown. The larvae finish feeding in late June or early July and then fall to the ground where they pupate.

Whitish with pale brown heads, the elf leaf miner larvae measure about 6mm in length. They overwinter in the soil and produces a brown papery cocoon. In the spring, they emerges as an adult sawfly.

Pesticides can control the spread of the elm leaf miner. Injected into the trunk after the leaves are fully formed, the pesticide will repel the larvae for about 2 months. As many chemical pesticides can be poisonous, care should be taken to read the label before use.

Natural predators can also help. Ground beetles, braconid wasps and ichneumonids all prey on the leaf miner during various stages of development. To attract these predators, introduce plant species such as evening primrose, evergreen eunymous, baltic, boston or english ivy, fennel or rue.

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See also www.asian-longhorned-beetle.com.

A wood-chewing insect from China is the newest threat to North America's elms.

Slightly larger than a cockroach, the Asian longhorned beetle chews its way into the trunks of the trees where it lays its eggs. Eventually, the tree dies.

Although elms will be affected, the primary target of this insect are maples. Loss of maple trees could have a considerable impact on the maple syrup industry.

Carried over from China in wooden skids, the beetle has made its presence felt in Chicago. Officials have begun extensive efforts to control further spread.

Source: Globe and Mail August 18, 1999

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Quick Elm Facts

CanadaUnited StatesInternational

Other Information LinksElms in the Media

Canada Manitoba

● Winnipeg's Coalition to Save the Elms● Manitoba Natural Resources

Forest Landscape Management, Forestry Branch

Nova Scotia

● Nova Scotia Provincial Regulation Registry● Halifax Regional Municipality, City of Dartmouth

Bylaw

Ontario

● Ontario Shade Tree Council

Saskatchewan

● Saskatchewan Environment and Resource Management

● CETAC-WEST● College of Agriculture, University of Saskatchewan

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United States National

● Department of the Interior, National Parks Service, Integrated Pest Management Dutch Elm Disease Manual

Colorado

● Colorado State University Cooperative Extension Plant Talk

Illinois

● Morton Arboretum in Chicago "A Brief History of Dutch Elm Disease"

● Des Plaines City Services

Iowa

● Iowa State University Horticulture and Home Pest News

Kansas

● Kansas State University Research and Extension

Kentucky

● Kentucky State University Extension Service

Michigan

● Michigan State University Extension Service

Minnesota

● University of Minnesota Center for Urban Ecology and Sustainability

Missouri

● University of Missouri-Columbia Extension

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Montana

● Montana State University Extension Service

North Dakota

● North Dakota State University Extension Service

Washington

● Washington State University Cooperative Extension, Western Washington

International International Links coming soon

Other Information Links

● Elms Return to Elm Street

Elms in the Media ● Smithsonian Magazine "Racing to Revive our Embattled Elms", June 1998.

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If you feel a link should be included here, please contact us.

Also, if you live in an area not listed above, we can do some research for you to see if we can find some helpful resources.

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Quick Facts

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Quick Elm Facts

● Trees add not only beauty but value to our property. The value of a mature elm for insurance purposes is US$2,500 (C$3,600).

● The 7,700,000 elm trees in urban centres in North America have a combined value of over US$19 billion

● Dutch elm disease got its name because it was discovered by scientists in Holland in 1917.

● The seven Dutch scientists who first identified Dutch elm disease were all women.

● Dutch elm disease hit England in the 1960’s and within 20 years had killed 17 million of the country’s 23 million elm trees.

● A second out-break of Dutch elm disease in 1945, destroyed second-generation elms in Eastern Canada and the United States. The elm population dropped from 77 million to 34 million by 1976.

● Fully mature elm trees can live as long as 300 years.

● The cooling effect of one urban elm tree is equivalent to five air conditioning units.

● North American settlers named the elm “the lady of the forest”.

● Elm trees first appeared in the Miocene period, about 40 million years ago.

● The American Elm grows to over 115 feet tall and can have a diameter in excess of ten feet.

● The Iroquois used elm bark to make canoes, rope and utensils

● The film “Nightmare on Elm Street” has absolutely nothing to do with elm trees

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This site is designed to be a comprehensive resource for homeowners, researchers and tree care professionals to find information about about elm trees.

● Quick Facts

● How to Care for Your Tree ● The Elmcare Newsletter - Sign up on the Homepage!

● Dutch Elm Disease

● The Elm's Place In History

● Links to elm tree resources

....and much more!

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This site is copyrighted by ArborScience. While we would be happy to share any of our information, we do require a written request.

Please note that while we have taken every effort to make sure that this site contains accurate information, we cannot be held responsible for any damages or problems arising from the use of the information that we have supplied.

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Safety FirstDead or dying branches can fall causing injury or property damage. Overgrown branches can obstruct lines of sight in vital areas such as intersections or driveways. Trees can come into contact with overhead power lines. Pruning removes safety hazards.

Better yet, by careful planting, you can avoid many of the potential hazards in the first place.

Maintenance Pruning Trees shed weak branches to promote growth in healthier areas. You can help this process. Remove branches that are in competition for sunlight or that are rubbing against other.

DED Preventative Pruning When an elm is under attack from the Dutch elm disease fungus, timely pruning of infected branches can check the spread of the disease.

Pruning should not take place from early April to late July when the beetle is active. After the limbs are removed they should be burned or buried.

For more information on DED preventative pruning, click here.

Types of Pruning

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Crown-thinning With this type of pruning, dead or dying branches are removed from the crown in order to allow better air movement and light penetration to the tree.

Crown-raisingThis type of pruning is performed to provide clearance. Most municipalities have bylaws specifying minimum branch height beside roads and sidewalks. The lower branches are removed effectively raising the crown of the tree.

Crown-reduction When a tree has outgrown the available space, crown-reduction pruning is often necessary. Upper limbs are pruned to either reduce the height or width of the crown.

Proper Pruning Techniques

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Adopting proper pruning techniques is vital for the health of the tree. Cuts should be made at the point where two branches meet (known as a node). Cuts made in the middle of a branch (internodal cuts) can result in unhealthy regrowth and slow wound closure.

Where To Make Your CutThe area where the branch meets a major limb is characterized by two features – the branch collar and the branch bark ridge. The branch collar is underneath the branch, while the branch bark ridge is above it. This is the point where branches would naturally be lost. When pruning a branch, it is important to make a cut as close as possible to these features without actually cutting them. Cutting into the branch collar will promote decay in the main stem as it takes longer for the tree to close such a wound.

Larger LimbsFor larger limbs, special care is required to prevent damage to the tree. If a cut is made from the branch ridge directly through to the branch collar, often the limbs weight will cause it to rip away from the stem leading to a large slow-closing wound. Therefore, first a small undercut should be performed a small distance (maybe 5cm) away from the collar. Then, a clean topcut can be made on the outside of the undercut (away from the stem). Finally, a clean cut can be made just outside the branch collar.

Timing

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When Unlike many other tree species, pruning must be done at a very specific time of year. Because open wounds attract the elm bark beetle (the major vector for Dutch elm disease), pruning should never be performed from about mid-April to late-July. In fact, some communities have bylaws to this effect. Also, due to presence of a variety of fungal spores in the fall, if possible, pruning should be avoided. This leaves early spring as an ideal pruning season. With the growing season to follow, the tree has ample time to close the wound and regain its vitality.

How Often Mature deciduous ornamental trees such as elms should be thoroughly pruned once every three years with annual minor pruning. In areas where Dutch elm disease is present, more vigilance is required to allow timely removal of dead or dying branches. If a tree is noticeably slow to bounce back from a pruning session, less frequent pruning may be in order.

Pruning Pitfalls

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Topping

This practice is extremely harmful to trees. Firstly, it involves the sudden removal of a large proportion of the tree’s foliage which temporarily starves the tree of needed energy. To compensate for the loss, the tree will promote the growth of new buds, usually from just below the stub. Homeowners may feel that this new growth represents healthy regrowth, but this is not the case. The new buds are structurally weak and superficially anchored to the larger branch. Although very quick to grow, they can easily break in windy conditions. Thus, the original purpose of topping (pruning potentially hazardous limbs or controlling upward growth) is defeated.

Secondly, bark that is suddenly exposed to large amounts of sunlight and heat can become scalded. This can lead to damage and often death of the limb. This again creates a potential hazard.

Thirdly, topping wounds close slowly and sometimes not at all. Insects and pathogens can therefore gain access to the tree for extended periods of time. This is a major concern if Dutch elm disease has been spotted in the region.

Finally, topped trees are unattractive and can often contribute to a lowering of property values.

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Leaves

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Leaves perform two vital functions for trees. They produce sugars by photosynthesis and they allow for the distribution of water through transpiration.

Photosynthesis is a process by which CO2 and water are combined with sunlight and a pigment called chlorophyll. The chemical reactions result in the production of sugars which provide energy to the tree. The leaves use some of this energy, but the majority is transported, in the form of sugar solutions, to other parts of the tree that require it.

Transpiration, or water loss, also takes place in the leaves. As this occurs, water is drawn up from the roots through the vascular system to replace lost moisture.

RootsBark

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Roots

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Jump ahead to: Root StructureRoot Growth

Roots are organs that provide structural stability for trees. Roots also absorb water and minerals.

Root Structure

Roots are made up of a number of specialized components. The root hairs, tiny structures extending from the main root stems, have very thin walls which absorb water and minerals. This mineral solution is passed into the vascular core of the root from where it is transported throughout the tree. At the tip of the root, there exists a protective structure called the root cap. These loose cells are shed as the root grows into the soil.

Different trees have slightly different root systems. Some trees, such as the pine, have a strong central root called the taproot. This is usually larger than any other roots and often extends deep into the ground. Because substantial damage to this root can be fatal to the tree, trees with taproots are generally difficult to transplant.

Other trees, such as the elm or maple, do not have a dominant taproot. Their root systems are characterized by a large number of roots often closer to the surface.

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Root Growth

Generally, root growth is influenced by moisture and gravity. In other words, unless there are substantial amounts of moisture near the surface, roots tend to grow downwards through the soil.

Roots are always growing and, like a tree's trunk, they grow both longer and wider. At the tip of the roots, the growing region is called the meristem. This is where most of the lengthwise growth takes place. In addition to this, wood is added to the inside of the root and phloem is added towards the outside.

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Roots

Source: MS Encarta online encyclopedia

LeavesBark

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Bark

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Bark is the outer protective covering of tree trunks. The form and structure of bark can differ greatly from tree to tree. As a result, it is a useful characteristic for tree identification.

Bark is made up of two layers - outer bark and inner bark.

The outer bark is made up of dead cells. This layer is usually quite thick, but in certain trees (young birch, for example) it is very thin.

The inner bark, known as the phloem is made up of a thin layer of living cells. These cells have extremely thin walls allowing water and nutrients (in the form of sugar solutions) to pass easily throughout the tree. Somewhat akin to human skin, old bark is shed, and new bark is formed from the inside.

LeavesRoots

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Ask the Experts

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Due to the overwhelming response we have been receiving, we are temporarily suspending the Ask the Experts section of elmcare.com. Our experts are currently in the field conducting trials for ELMguard and are unable to keep up with the number of questions we are receiving.

Please check back frequently or enter your e-mail address below to be informed when the Ask the Experts section is reopened.

Perhaps your question has already been answered. Check the categories below for past questions and answers.

Fertilizing (4) Watering Insects (1)

Elms in general (5) Dutch elm disease (5) Pruning (2)

Other diseases (2) Elm Wood (2) new!

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Ask the Experts - Fertilizing

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Should I be using fertilizer for my tree?

Will my lawn fertilizer help my elm tree?

When should I fertilize my elm?

What formulation would you recommend for an elm tree?

Question

Should I be using fertilizing for my tree?

Answer Fertilizing is an integral part of a comprehensive elm care program. Elms trees that live in a city lack some of the nutrients it needs to

truly do well.

Question Will my lawn fertilizer help my elm tree?

Answer Probably not. Lawn fertilizer has several characteristics which make it undesirable for elms. First, it's generally in a granular formulation. For trees, you want a fertilizer you can put into the ground. Secondly, the formulations often include chemicals to kill weeds. This can be harmful for the tree. Thirdly, grass competes with a tree for available nutrients. Because of this, nutrients will be absorbed by the grass before they can penetrate the soil to the tree's roots. You should use a fertilizer specially formulated for trees.

Question When should I fertilize my elm?

Answer Fertilization should be done in the spring or the fall. Fall is very good because there is a lot of moisture in the ground and the roots are

very active.

Question What formulation would you recommend for an elm tree?

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Ask the Experts - Fertilizing

Answer A 5-10-10 or 6-12-12 fertilizer would be ideal for an elm. The first number is the proportion of Nitrogen. You don't want as much Nitrogen because that is the mineral that promotes new growth. If you have too much new growth, the tree can't focus as much on other important tasks such as building up its defense mechanism.

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How should I water my elm tree?

Question

How should I water my elm tree?

Answer When you are watering your tree, you want to get the moisture below the turf line (below the grass roots). Because of this, a sprinkler is not very effective. One method is to simply soak the ground with a hose. This allows the water to penetrate to the tree roots.

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What should I do to control the elm bark beetle population?

Question

What should I do to control the elm bark beetle population?

Answer Elm bark beetles are the major vector of Dutch elm disease. They carry the fungus on their backs and burrow into elm trees. There are a number of insecticides that are registered for use in controlling the elm bark beetle population.

It is estimated, however, that less than 5% of elm bark beetles actually carry the fungus. The presence of the beetles does not necessarily indicate the presence of Dutch elm disease. Also, it is important to consult a professional applicator before using insecticides.

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Ask the Experts - Elms in General

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Can I separate two elms that have grown together?

How suitable is the Siberian elm as a windbreak?

How do I remove stumps?

What causes the bark to peel away?

Do elm trees lose their leaves in Florida?

Question

Can I separate two elms that have grown together?

Answer Probably the best solution would be to pick the best one, keep it and remove the other. I hate to suggest that you cut one seedling, but you will only have problems if you leave them together. I fear that if you try to separate them you may lose both.

Question How suitable is the Siberian elm for use as a windbreak?

Answer I would have to say the Siberian elm is considered a weed species in many cities. It is extremely hardy and will grow out of a crack in the pavement with very little soil available. It is a 'dirty' tree that sheds branches, leaves, seeds etc. , almost continually. If you are committed to maintenance then it can be used as a windbreak, but if the tree is left to grow without pruning it will soon become unmanageable and unsightly. The species is best used as a hedge species.

Question How do I remove stumps?Answer Have someone come with a stump grinder and grind it down al least

6 inches below the grade. If that doesn't work, there are over-the-counter products available at most garden centers that inhibit any new sprouting.

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Ask the Experts - Elms in General

Question My elm tree seems healthy, but I've noticed that there are large tracts of bark running vertically from the base up to 3-4 feet that can be easily peeled away. What may have caused this and what should I do?

Answer When elms get to be larger in diameter, there is a tendency for outer bark to loosen to allow for the expansion of the tree. This is also why bark tends to be furrowed in appearance. Generally, as this is a natural occurrence, you need not take any special action. To be sure, however, it is always a good idea to consult a qualified arborist.

Question I live in Florida and I recently bought two elm trees. They both lost

the majority of their leaves. Do elm trees usually lose their leaves this far south?

Answer American elms are deciduous broadleaf trees and as such, they lose their leaves in the fall. In the natural habitat, I haven't heard of any instance where they kept their leaves for the winter. When they are transplanted into an area with a warmer climate such as Florida, however, they could potentially act quite differently.

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Ask the Experts - Dutch Elm Disease

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Is Dutch elm disease a problem in Texas?

How long can DED remain dormant?

Can you use dead elms for furniture?

Are some species more resistant to DED?

Can Nystatin be used to treat DED?

Question

Is Dutch elm disease a problem in Texas?

Answer From what I can gather, there is an extremely low incidence of DED in Texas. I was told that there is usually at least one confirmed case a year in Texas, but there has been no significant wholesale loss of elms due to DED. The native Cedar elm seems to display some level of resistance to DED but I do not believe that this has been extensively tested. The American elm is not a prevalent species in the state.

Question How long can Dutch elm disease remain dormant in elm trees?

Answer I found out that in one study, the researchers isolated the fungus in vessels in the tree that had been effectively sealed off in the tree for 25 years. The fungus that was isolated was still viable. If this occurs in trees it is generally not a threat to survival if the defense reactions effectively isolate the disease by the end of the growing season. If, however, the defense reactions are not complete, the fungus may be able to reach the newly forming vessels in the next growing season. When this happens there is a much higher likelihood that the disease will affect the entire tree and eventually kill it.

I must point out that this is not a common occurrence.

Question My Siberian elms died. I don't think it was Dutch elm disease and I

want to use the wood for furniture. Is it safe?

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Ask the Experts - Dutch Elm Disease

Answer Generally, DED does not kill Siberian elm trees. Usually only one branch will die as the species can effectively fend off the disease. I would be fairly certain that your trees are not infected with DED. If you remove all of the bark there should be no risk of bark beetles breeding in the wood. You should check with the local authorities, however, as there may be bylaws restricting the use of elm wood.

Question Are some elm species more resistant to Dutch elm disease than

others?Answer Yes. Species that have coexisted with the Dutch elm disease fungus

for the longest period tend to have the highest degree of resistance. These species have evolved to develop better defenses against the pathogen. Scientists now believe that Dutch elm disease originated in central Asia. Therefore, we would expect that species originating from Asia would show an increased resistance to DED and in fact that is what we do see. The Siberian elm, for example, is largely resistant. Species such as the American elm, however, have only recently come into contact with the disease and as such have not had the time to develop immunity.

Scientists are now working towards developing cultivars which exhibit greater resistance to Dutch elm disease. The Liberty Elm is one such cultivar.

Question I have heard of an antifungal called Nystatin. Can it be used to treat

Dutch elm disease?Answer Because Nystatin is an antifungal, it could conceivably have an effect

on Dutch elm disease. The drug was, however, designed for use on humans and is relatively expensive to procure. A major concern about the use of Nystatin arises from the fact that it is an antibiotic. As a result, overuse can lead to more aggressive strains of the fungus.

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Ask the Experts - Pruning

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Does pruning make a tree grow faster?

Why can't I prune in my municipality?

Question

Does pruning make a tree grow faster?

Answer I'm not sure that pruning will help the tree to grow faster, but it will help if you prune out weak, crossing and interfering branches and direct future growth into the good structure. Ideally you should keep as much foliage as possible so that the tree can produce and establish a solid root system - especially when the tree is young. I would consult a local arborist before you do any pruning.

Question There is a law in my municipality against pruning an elm tree, but

other trees can be pruned. Why is that? Answer

That's a good question. The answer lies with the way that Dutch elm disease is transmitted. The elm bark beetle, which carries the DED fungus on its back, is most active from mid-spring until late summer. These beetles are attracted to the open wounds that are left on a tree after pruning. Therefore, you should only prune an elm when the beetles are relatively inactive which is in early spring or fall.

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Ask the Experts - Other Diseases

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How do I know if my tree has elm yellows?

What can I do if my tree has wetwood?

Question

How do I know if my tree has Elm Yellows?

Answer You can test for elm yellows by cutting a small potentially infected branch and placing it in a sealed glass jar. After a couple of hours, open the jar and smell inside to see if you detect a wintergreen odour. This is a telltale sign.

If your question isn't answered here, send it to us!Or visit the elm yellows section of elmcare.com.

Question What can I do if my tree has wetwood?Answer In, general, there is not a lot that you can do about Wetwood.

Wetwood is caused by a bacterial infection and is very common in elms and many other species. The infection causes moisture to be retained in the wood and also produces metabolic gases that increase the internal pressures in the tree. Periodically the liquid will be forced out of the tree through wound sites. The liquid oozes out and down the tree, where other organisms colonize it. This liquid is called slime flux and is known to have a foul odour.

Wetwood becomes a problem only when enough infection sites occur on the tree to compromise its structural integrity. A professional or consulting arborist should judge this. Otherwise, wetwood can be viewed as somewhat beneficial, as the moist environment that it creates in the tree helps to prevent decay fungi from colonizing the tree.

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Ask the Experts - Other Diseases

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Ask the Experts - Wood

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Can I use elm firewood given to me by a tree removal company?

Is furniture made of elm wood prone to cracking?

Question

Can I use elm firewood given to me by a tree removal company?

Answer I would be very concerned about the wood and the possibility of disease. Tree companies will often have trouble disposing of wood and will jump at the opportunity of giving it away rather than hauling it away. Many of them are rather unscrupulous and will tell you what you want to hear if it is in their best interest. You could very well spread the disease in your area by having the wood there. Many jurisdictions have strict bans on elm firewood with stiff penalties if it is found on your property. There is a characteristic streaking of the wood that can be seen in infected branches, but sometimes that is hard to detect if you are not familiar with the symptom. If the wood is very dry and the bark is loose or absent then there is little to be concerned about. If not, then you could have a problem. Elms are very vigorous trees and don't die very easily, so I wonder why the tree died if it was not DED. I would suggest contacting a local urban forester or a consulting arborist ASAP, as the bark beetles that transfer the disease will fly to healthy trees any time soon. This could be a serious problem for your neighbourhood.

Question Is furniture made of elm wood prone to cracking in dry areas?

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Ask the Experts - Wood

Answer It seems that if that much time has been taken to dry the wood it should be fairly dry. The only question remaining is whether it was dried outside or inside. If outside, it will probably have about 15% residual moisture and that can drop to 4-5% inside in the driest time of the year. The other question raised is how was the piece cut? If the slice was made along the grain of the wood there is a much lower likelihood that it will split than if the piece was cut on an angle across the grain. You should also see how the final finish has been applied and how well all the surfaces have been sealed. The finish should be highly impermeable to moisture.

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Identifying Silhouette

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The American elm is one of the largest trees in eastern North America and it grows to a height of 35m with a trunk diameter of 175cm. The base of the tree is reinforced by prominent root flares and a shallow and wide-spreading root system. A few large upright limbs support many outwardly fanning branches.

The tips of these branches often droop downwards contributing to the overall graceful umbrella-like silhouette. Fully mature trees can live as long as 300 years, although in areas which have experienced Dutch elm disease, young trees less than 30 years old are the norm.

LeavesBark

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Identifying Leaves

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Elm leaves are deciduous and alternate in two rows along the shoot. The shape is oval and tapers towards a point. The edge is ragged and saw-toothed and veins are prominent. The size is dependent on the species, but the leaves of an American elm are usually between 10 and 15 cm in length.

Notice the uneven base on each leaf. This characteristic is common in elms and is a good thing to look for.

SilhouetteBark

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Identifying Bark

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The bark of an American elm is dark grayish-brown becoming mottled ash-gray as the tree ages. The surface is deeply furrowed with broad obliquely intersecting ridges.

SilhouetteLeaves

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The Cultivated Elm

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Long Ago

We have been using the elm tree for thousands of years since the first farmers found them in ancient forests.

In western Europe, farmers used elm leaves and branches as cattle feed. Fisherman traded for elm leaves to boil and eat in times of scarcity.

Romans used living elms to support their grapevines - a practice called "marrying the vine to the elm." They also selectively bred elms producing many of the species we see today throughout their former Empire.

In North America, the Iroquois used the bark of elms to make canoes, rope, utensils, and roofing for their homes. The Ainu, native people of Japan, used elm bark for clothing.

Luxurious Shade

Until recently, elms were the predominant shade tree in North America.

Elms, like other shade trees, are nature’s air conditioners. They help to cool not just by providing shade but by the transpiration of water from their leaves. In fact, the cooling effect of one urban elm tree is equivalent to five air conditioning units.

And like all trees, elms are a natural air purifier converting carbon dioxide into oxygen.

Rural Roots

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The Cultivated Elm

The hardy elm trees readily endures the severe winters of the US Midwest and the Canadian Prairies.

Shelterbelts of elm trees provide shade for livestock and protect farms from biting winds and storms.

Because their wood is particularly tough, farmers often left elms standing when clearing fields. To this day, you can see solitary elms in the middle of large open fields.

Industrial Benefits

The tough cross-grained wood of the elm tree is highly resistant to splitting. It is used to make baskets, furniture, and flooring. Hockey sticks, wheel hubs and boat frames have all taken advantage of the special properties of elm wood.

A Special Affection

Appreciation of the elm tree is evidenced by North American settlers, who named the elm “the lady of the forest”. Countless poems have been penned about the stately giant.

It also figures in many historical events. For example, George Washington first drew his sword underneath the Washington Elm in 1775. Poet James Russell Lowell wrote of Washington: “What figure more immovably august, Than that grave strength so patient and so pure.” (Atlantic Monthly: 1875 36)

What better words to describe the elm itself?

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Living History

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From the Liberty Elm in Boston to the Wolseley Elm in Winnipeg, elms have been focal points of community and political action.

Click on one of the following to learn more:

The Liberty Elm The Wolseley Elm The Washington Elm William Penn's Elm

Courtesy APS (www.scisoc.org)

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Liberty Elm

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Boston's Liberty Elm is arguably the first symbol of freedom for the United States. It was a backdrop to oration, celebration, and revolution.

On August 14, 1765, colonists hung effigies of Lord Butte and Andrew Oliver in protest against the despised Stamp Act. Revolutionaries held rallies and speeches around the tree.

It was cut down by departing British soldiers in 1775.

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Wolseley Elm

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In Winnipeg, Manitoba, in the late 1950's, city officials wanted to remove a majestic elm to make way for a new street. Outraged, a group of women locked arms around the tree in protest. The city backed down and the tree was saved.

Years later, the tree was lost to vandalism. But after it was taken down, a new elm was planted to take its place.

The Wolseley Elm is now part of Winnipeg's folklore.

Source: Manitoba's "Coalition to Save the Elms." (www.savetheelms.mb.ca)

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Washington Elm

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George Washington took control of the revolutionary army and first drew his sword underneath this tree in 1775.

The tree died in 1923.

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Library of Congress, Prints and Photographs

Division, Detroit Publishing Company Collection

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William Penn's Elm

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William Penn signed the Treaty of Shackamaxon with the Delaware Indians underneath a huge elm.

This treaty formalized the purchase of land in Pennsylvania. It also marked the beginning of an amicable relationship between the Quakers and the Indians that lasted for almost a hundred years.

In 1810, a storm blew the tree down. It was a grand 280 years old. Today, items made from the wood of that elm are considered valuable antiques.

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Elms in Literature

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The elm has enchanted and inspired poets for countless generations.

Click on a name to read more:

Robert Frost John Milton

Ralph Waldo Emerson Robert Browning

Herman Melville Erasmus Darwin

Denise Levertov William Butler Yeats

Phillip Freneau Alfred Tennyson

William Wordsworth Sylvia Plath

John Clare Oliver Wendell Holmes

Ovid Virgil Theocritus

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Robert Frost

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Robert Frost (1874-1963)

From "The Cocoon"

As far as I can see, this autumn hazeThat spreading in the evening air both waysMakes the new moon look anything but newAnd pours the elm-tree meadow full of blue,Is all the smoke from one poor house alone.

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John Milton

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John Milton (1608-1674)

From "Comus"

Perhaps some cold bank is her bolster now,Or 'gainst the rugged bark of some broad elmLeans her unpillowed head fraught with sad fears

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Ralph Waldo Emerson

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Ralph Waldo Emerson (1803-1882)

From "Compensation"

Man's the elm, and Wealth the vine,Stanch and strong the tendrils twine

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Robert Browning

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Robert Browning (1812~1889)

"Oh, to be in England"

Oh, to be in EnglandNow that April's there,And whoever wakes in EnglandSees, some morning, unaware,That the lowest boughs and the brushwood sheafRound the elm-tree bole are in tiny leafRound the chaffinch sings on the orchard boughIn England - now!

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Herman Melville

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Herman Melville (1819-1891)

From "Malvern Hill"

We elms of Malvern Hill Remember everything;But sap the twig will fill: Wag the world how it will,Leaves must be green in Spring

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Erasmus Darwin

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Erasmus Darwin (1731~1802)

From "Untitled"

Herb, shrub, and tree, with strong emotions riseFor light and air, and battle in the skies;Whose roots diverging with opposing toilContend below for moisture and soil;Round the tall Elm the flattering Ivies bend,And strangle, as they clasp, their struggling friend.

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Denise Levertov

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Denise Levertov (1923-1997)

"Living While it May"

The young elm that must be cutbecause its roots push at the house wall

taps and scrapes my windowurgently - but when I look round at it

remains still

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Denise Levertov by David Geier

Photography

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William Butler Yeats

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William Butler Yeats (1865~1939)

From "My House"

An ancient bridge, and a more ancient tower,A farmhouse that is sheltered by its wall,An acre of stony ground,Where the symbolic rose can break in flower,Old ragged elms, old thorns innumerable.

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Phillip Freneau

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Phillip Freneau (1752~1832)

From "The Indian Burying Ground"

Here still an aged elm aspires,Beneath whose far-projecting shade(And which the shepherd still admires)The children of the forest played.

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Alfred Tennyson

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Alfred Tennyson (1809~1892)

From "Untitled"

And gathering freshlier overhead Rocked the full-foliaged elms, and swung The heavy-folded rose, and flungThe lilies to and fro, and said,

"The dawn, the dawn," and died away; And East and West, without a breath, Mixt their dim lights, like life and death,To broaden into boundless day.

From "Come Down, O Maid"

Sweeter thy voice, but every sound is sweetMyriads of rivulets, hurrying through the lawn,The moan of doves in immemorial elms,And murmuring of innumerable bees.

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William Wordsworth

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William Wordsworth (1770~1850)

From "Untitled"

Thither I came, and there, amid the gloomSpread by a brotherhood of lofty elmsAppeared a roofless hut, four naked wallsThat stared upon each other...

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Sylvia Plath

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Sylvia Plath (1932~1963)

"Elm"

I know the bottom, she says. I know it with my great tap root; It is what you fear. I do not fear it: I have been there.

Is it the sea you hear in me,Its dissatisfactions? Or the voice of nothing, that was you madness?

Love is a shadow. How you lie and cry after it. Listen: these are its hooves: it has gone off, like a horse.

All night I shall gallup thus, impetuously,Till your head is a stone, your pillow a little turf, Echoing, echoing.

Or shall I bring you the sound of poisons? This is rain now, the big hush. And this is the fruit of it: tin white, like arsenic.

I have suffered the atrocity of sunsets. Scorched to the root My red filaments burn and stand,a hand of wires.

Now I break up in pieces that fly about like clubs. A wind of such violence Will tolerate no bystanding: I must shriek.

The moon, also, is merciless: she would drag me Cruelly, being barren. Her radience scathes me. Or perhaps I have caught her.

I let her go. I let her go Diminished and flat, as after radical surgery. How your bad dreams possess and endow me.

I am inhabited by a cry.

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Sylvia Plath

Nightly it flaps out Looking, with its hooks, for something to love.

I am terrified by this dark thing That sleeps in me; All day I feel its soft, feathery turnings, its malignity.

Clouds pass and disperse. Are those the faces of love, those pale irretrievables? Is it for such I agitate my heart?

I am incapable of more knowledge. What is this, this face So murderous in its strangle of branches?--

Its snaky acids kiss. It petrifies the will. These are the isolate, slow faults That kill, that kill, that kill.

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John Clare

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John Clare (1793-1864)

From "The Elm Tree"

Old favourite tree thoust seen times change But change till now did never come to thee For time beheld thee as his sacred dower And nature claimed thee her domestic tree.

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Oliver Wendell Holmes (1809-1894)

The hubs of logs from the Settler's ellum, Last of its timber, they couldn't sell'em, Never an axe had seen their chips, And the wedges flow from between their lips, Their blunt ends frizzled like celery tips.

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Ovid

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Ovid (43 B.C.~A.D. 17)

If that fair elm alone should stand, No grapes would glow with gold and tempt the hand, Or if that vine without her elm should grow, T'would creep, a poor neglected shrub below.

From "Untitled"

Help bucksome God then! so may the lov'd VineSwarm with num'rous grapes, and big with WineLoad the kind Elm, and so thy Orgyes beWith priests lowd showtes, and Satyrs kept to thee!

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Virgil

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Virgil (70~19 B.C.)

From "Untitled"

And great gods eke aggrievèd with our town.I saw Troye fall down in burning gledes,Neptunus' town clean razèd from the soil,Like as the elm forgrown in mountains high,Round hewen with axe, that husbandmenWith thick assaults strive to tear up, doth threat,And hackt beneath trembling doth bend his top,Till gold with strokes, giving the latter crack,Rent from height, with ruin it doth fall.

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Theocritus

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Theocritus

From "The Death of Daphnis"

Then rest we in the shadow of the elmFronting Priapus and the Fountain-nymphs.

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Elms in Mythology

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Elm trees have entered our mythology - a mark of their prominence in the lives of early civilizations.

Germanic tribes included the elm in their creation myth, and Mongols incorporated it in a wedding prayer.

Germanic Creation Myth

The ancient Germanic peoples who came to inhabit much of Europe, believed that three gods, Odin, Vili and Ve, created the world.

According to the myth, these three gods were walking by the sea examining their handiwork when they came upon two fallen trees. One was an ash, the other an elm. Odin imbued them with the spark of life. Vili endowed them with spirit and a thirst for knowledge. Ve gave them the gift of five senses.

When they had finished, the fallen trees resembled the gods themselves. Out of the ash came man. Woman was created from the elm and her name was Embla.

(Source: "Mythologies" compiled by Yves Bonnefoy v. 1, p.281)

Mongol Wedding Prayer

"Mother Ut (Fire), Mistress of Fire, descended from the elms on the tops of the Khangai-Khan and the Burkhatu-Khan mountains. Thou, who wast born when Heaven and Earth parted, who camest forth from the footprints of Mother Ötygen (Earth), thou creation of Tengeri-Khan. Mother Ut, thy father is the hard steel, thy mother the flint, thy ancestors, the elm trees. Thy brightness reaches the heavens and spreads over the earth. Thy brightness reaches the Heaven-dweller, nursed by the Mistress Uluken.

Goddess Ut, we offer thee yellow butter and a yellow-headed white sheep. Thine are this brave boy and the beautiful bride, the slender daughter."

(Source: "Mythology of All Races" vol. iv, Uno Holmberg, p.453)

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Although we cannot answer every e-mail we receive, we will read every one and do our best to reply.

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The American Elm and Dutch Elm Disease

M. HubbesFaculty of Forestry, University of Toronto

Abstract

Shortly after World War I, a new disease previously unknown among elms, emerged in Holland. It spread rapidly from Europe to Great Britain (1927), United States (1930), and Canada (1945), killing millions of elms. The disease known, as

Dutch elm disease (DED) is a wilt disease, caused by the fungus Ophiostoma ulmi. It is transmitted from tree to tree by elm bark beetles (scolytid) vectors.

Numerous attempts to control the disease have concentrated on the reduction of insect vector populations, exploitation of natural host resistance, extensive

application of fungicides and integrated pest management. In spite of these efforts in Canada, the disease continues to migrate westwards threatening the elm

populations in Saskatchewan and Alberta. Today there are approximately 700,000 elm shade trees in cities and towns across Canada and their value exceeds $2.5

billion dollars.

With the advance of molecular biology new, powerful tools are now available to study, in greater detail, the molecular and biochemical mechanisms of the DED

pathogen, with particular reference to the mechanisms that induce host defenses. A glycoprotein, has been isolated and identified such that when injected either in

liquid or pellet form into the elm tree, significantly reduced the wilting symptoms of both 5 year old elm seedlings and 10 cam diameter trees. The elicitor induces a

chain of defensive reactions that prevent the rapid spread of the fungus within the vascular system of the host.

Click here to view the entire article.

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The American Elm and Dutch Elm Disease

M. HubbesFaculty of Forestry, University of Toronto

Abstract

Shortly after World War I, a new disease previously unknown among elms, emerged in Holland. It spread rapidly from Europe to Great Britain (1927), United States (1930), and Canada (1945), killing millions of elms. The disease known, as Dutch elm disease (DED) is a wilt disease, caused by the fungus Ophiostoma ulmi. It is transmitted from tree to tree by elm bark beetles (scolytid) vectors. Numerous attempts to control the disease have concentrated on the reduction of insect vector populations, exploitation of natural host resistance, extensive application of fungicides and integrated pest management. In spite of these efforts in Canada, the disease continues to migrate westwards threatening the elm populations in Saskatchewan and Alberta. Today there are approximately 700,000 elm shade trees in cities and towns across Canada and their value exceeds $2.5 billion dollars.

With the advance of molecular biology new, powerful tools are now available to study, in greater detail, the molecular and biochemical mechanisms of the DED pathogen, with particular reference to the mechanisms that induce host defenses. A glycoprotein, has been isolated and identified such that when injected either in liquid or pellet form into the elm tree, significantly reduced the wilting symptoms of both 5 year old elm seedlings and 10 cam diameter trees. The elicitor induces a chain of defensive reactions that prevent the rapid spread of the fungus within the vascular system of the host.

Introduction

Almost 80 years ago Dutch scientists reported the dramatic appearance of a new disease on elms in Holland. The disease quickly became known as Dutch elm disease (DED). It is caused by the fungus Ophiostoma ulmi (sensus lato), and has claimed the life of millions of stately elm trees in Europe and North America. Elms, and in particular the American elm (Ulmus americana), have been an

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unmistakable cultural and historic landmark of the North American continent. The tree’s tall and majestic growth combines beauty and grace, placing it among the most desirable shade tree in our cities and villages. Planted along boulevards and streets, their crowns span roads and houses providing clean air, coolness during hot summer days and shelter against UV radiation. The New York Times, in a February 26, 1989 article, claimed that a large tree is equivalent to five air conditioning units, playing a very important energy conservation role in our ecosystem.

Shortly after World War I, in 1918, a new, previously unknown disease of elms emerged in Holland, which caused yellowing and then wilting of leaves as well as rapid tree death. The disease spread like a plague and traveled quickly from Europe to Great Britain (1927) and reached the United States in 1930 (Campana and Stipes 1981). Although some tree losses occurred in 1927 in England, it was the appearance of a new strain of the plague in the late 1960s that severely decimated the elm populations (Gibbs 1981). By 1980, 17 million of the 23 million previous existing elms had been killed in southern England, causing extensive economic, esthetic and environmental losses.

Around 1930 there were approximately 77 millions elm trees in cities and towns across North America. The introduction of the disease had a devastating effect. For example, by 1976 municipalities in the northeastern United States lost 56% of their original elm population (Huntley 1982).

Equally significant, a second introduction of the disease to the North American continent at Sorell, Quebec, Canada in 1945 (Pomerleau 1981) initiated one of the largest mass destruction of trees ever witnessed, particularly when the disease fronts from the US and eastern Canada met to migrate westwards. Of the 77 millions elms in the US prior to the disease introduction, only about 34 million survived by 1976. In Canada the eastern provinces, New Brunswick, Quebec, and Ontario also suffered major losses. More than 600,000 elms were quickly killed in Quebec and Toronto’s 35,000 elm tree population was rapidly reduced by 80% (Huntley 1982). Presently the disease front has reached the elm populations of Saskatchewan and threatens those of Alberta. This situation causes great concern to private citizens as well as provincial and municipal authorities. In the prairie provinces, elms constitute the majority of shade trees in cities and villages. No other tree is better suited than the elm to withstand the harsh winter climate and urban environmental stresses in these regions, with its high winds, extreme temperatures and road salt. Therefore the great efforts of the City of Winnipeg for example to save their elms through a fully integrated management program, allows the City to claim itself as the City of elms. However, in spite of this, successful control programs after 21 years the losses of trees due to DED went from 2.5% to near 5.0% annually in 1996. Winnipeg’s American elm population still exceeds 200,000 in number. Today there are about 700,000 elms as shade trees in cities and towns across Canada and their value well exceeds $2.5 billion. The average elm tree value is based on the data given by Westwood (1991).

Disease control

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The DED fungus is mainly transmitted from tree to tree by the European elm bark beetle Scolytus multistriatus and the native elm bark beetle Hylurgopinus rufipes (Parker et al. 1947, Jin et al. 1996). Infection, by DED usually occurs from late May to July while the trees are producing “early wood” in the form of large vessel cells (Pomerleau 1968, Smalley and Guries 1993). Therefore, the spring-maturating adults of the European elm bark beetles and the over wintering adults of native elm bark beetles are the most common vectors of the disease (Pomerleau 1965, Lanier 1978, Lanier and Peacock 1981, Webber 1990). In addition the fungus may also move internally from tree to tree through root grafts (Stipes and Campana 1981).

Numerous attempts to control the disease have concentrated on three processes: reducing the vector populations namely the elm bark beetles (Lanier 1978, O’Callahan and Fairhurst 1983, Jin et al. 1996), the exploitation of natural host resistance (Ouellett and Pomerleau 1965, Holmes 1976, Lester 1978, Stipes and Campana 1981, Heybroek 1983, Smalley and Guries 1993, Ware and Miller 1997), and extensive application of fungicides (Smalley 1978, Stennes and French 1987). For the most part, these efforts have not produced the expected results of DED control (Stipes and Campana 1981, Sticklen et al. 1991).

Reduction of vector populations

Control of elm bark beetles, via chemical insecticides still seems the preferred choice in areas of high beetle populations to reduce the inoculum potential. However, in the long run this option is not viable because of the potential negative impact of the chemical insecticides to the environment and therefore can only be recommended for very specific situations. Particular attention must also be given to the selection of correct application equipment otherwise spraying is not very effective (Roy et al. 1988). The use of biological control agents such as insect parasitic (entomopathogenic) nematodes against bark beetles has not yet been exploited and awaits further development (Tomalak et al. 1989). The same is also true for the Lepidopteran BT toxins (Sticklen et al. 1991). The use of pheromone traps for vector control has great attraction from an environmental point of view. However it did not gain the expected momentum because the results were not as anticipated (Birch et al. 1981, Sticklen et al. 1991). Lanier (1989) reported on the usefulness of elm bark beetle trap trees for control of DED. This method seems very appealing, but awaits its wider testing application and has little use in many towns and cities because trees cannot be spared for traps. Sanitation, though expensive, is imperative for a successful DED control program, by removing infected tree parts, or dead trees that harbor beetle populations as well as the perfect and imperfect stage of the fungus. If not removed and destroyed, these dead trees are a major source of inoculum. However, sanitation alone is unable to halt the progress and spread of the disease (Pomerleau 1981).

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Chemical control

The introduction of several benzimidazole systemic fungicides has prompted a number of investigations on the effect of these compounds for DED control. Of these, benomyl has been tested against O. ulmi (Kondo et al. 1973). Another chemically related compound known as “Arbotect 20-S” has also been reported as active against the fungus (Smalley 1978, Prosser 1998). Attempts to overcome uptake and solubility problems caused by the tree were made by injecting the chemical into the stem or by uptake experiments through the roots (Kondo 1978, Roy et al. 1980). Compartmentalization of the tree (Shigo and Campana 1977), in response to wounding during injection, solubility problems with the chemical, as well as the ability of the pathogen to develop resistance against the fungicide (Bernier and Hubbes 1990a, b, Schreiber 1993), and economic reasons did not lend themselves for very large scale application of these fungicides.

Dutch elm disease is a vascular disease. To effectively colonize its host, the DED fungus has to invade a large number of vessels and can therefore not rely on its passive travel in the transpiration stream of a limited number of vessels. It has to spread from vessel to vessel. Pit membranes are the places where this can occur. Spores have to germinate and their hyphae penetrate through the membranes. Scheffer et al. (1988) reported that sterol biosynthesis inhibitors that interfere in the hyphae formation in O. ulmi suppressed disease development in two Dutch elm clones. Among a number of chemical derivatives fenpropimorph gave the best results. The problem is that this chemical renders the tree frost sensitive. Very recently another compound, a triazole derivative fungicide propiconazole, also known as “Alamo”, has been introduced for DED control. It is too soon to judge its effectiveness. Some tests appear encouraging, while others were not as successful as those were with “Arbotect 20-S” (Prosser 1998). However the manufacturer has withdrawn this latter product from the Canadian market.

Natural host resistance

The prospects for developing trees with genetic resistance to DED range from uncertain (Ouellett and Pomerleau 1965, Holmes 1976) to very well (Heybroek 1993, Smalley and Guries 1993, Smalley et al. 1993, Ware and Miller 1997). Earlier efforts to select and breed American elms (Ulmus americana) for DED resistance were disappointing. All North American species (U. rubra, U. thomasii, U. alata, U. serotina, and U. erassifolia) are susceptible to DED. U. americana is the most susceptible. Therefore efforts were also directed towards the development of genetic combinations from European and Asian gene pools (Smalley and Guries 1993, Smalley et al. 1993, Townsend and Santamour 1993, Sherald 1993, Ware and Miller 1997). A number of selections with superior resistance to DED were made of which the American “Liberty” elms were the most promising ones. There is a problem with these selections, as the basis for their resistance is unknown to scientists and therefore no estimates can be made as to whether this resistance will last or not. Small changes in the genetic background of

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the fungal population or changes in the physiology of the host as it ages may cause loss of resistance. Indeed, the DED fungus attacks some of the formerly resistant “Liberty” elms (A.L Shigo, personal communication).

It has been debated how the DED fungus kills its host. I believe that , a final solution to these problems can only be expected through application of modern methods of molecular biology by identification, isolation and subsequently directed rearrangement of genes controlling pathogen (DED) virulence and genes governing the host’s defense. Once the genetic bases of pathogen virulence and host resistance have been clarified, trees with long term tolerance towards the pathogen can be developed (Hubbes 1981, 1993). This for example has been achieved by the Siberian elm (U. pumila) probably through natural selection.

The fact that the Asian elms show resistance towards DED led to the assumption that DED originated in Asia. Recent investigations place its origin in the Himalayas (Brasier and Mehrotra 1995).

Although the development of resistant elms may satisfy the long-term strategy of DED control, effective protection of the existing elm populations in our cities and villages still remains a problem. In the past, there has been no lack of efforts to control the pathogen by biological means with the use of antagonistic microorganisms such as bacteria (Mazzone et al. 1982, Strobel and Myers 1982, Holmes and Plourde 1982, White 1982, Shi and Brasier 1986), fungi and virus particles (Hoch et al. 1985, Rogers et al. 1986, Webber 1987, Bernier et al. 1996). Some of the organisms showed promise, but their broad application as control agents has not yet been achieved. It is surprising that most of these treatments were conducted solely with the view to inhibit the fungal growth by direct antagonism, while the role of the host’s defense reactions was ignored. Field observations show that some trees have the means to defend themselves successfully against the invasion of the DED pathogen by restricting the spread of the fungus in their vessels. We assume if the mechanisms of this defense reaction could be clarified and their genetic basis understood they might well form a solid basis for disease control and resistance breeding.

The pathogen and its strains

In the early 1970’s, the observation that the population of O. ulmi was composed of two major group of strains, the aggressive and non-aggressive group, gave rise to numerous assumptions to explain pathogenicity and virulence (Gibbs et al. 1972, Bernier 1983). The non-aggressive isolates induce slower development for foliar symptoms during the first year of infection, a difference that tends to disappear during the second year (Schreiber and Townsend 1976). Scala et al. (1997) reported similar results. Isolates of the aggressive group very quickly induce severe wilting symptoms leading to the death of the hosts.

Aggressive and non-aggressive group of isolates also differ in a wide range of

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morphological and physiological characters. Crossing between the two groups is believed to be rare under field conditions (Gibbs and Brasier 1973, Brasier 1977, 1979, 1982). The aggressive group has been further subdivided in two races termed as the European (EAN) and North American (NAN) races (Brasier 1988). Initial separation of the isolates into the various sub-groups based on morphological characters was often erratic. Various well known laboratory techniques to identify isolated strains such as isozyme and protein patterns as well as restriction fragment length polymorphisms (RFLPs) and DNA fingerprinting have proven to be a very reliable approach to accurate strainal characterization (Bernier et al. 1983, Jeng and Hubbes 1983, Bates et al. 1989, Jeng et al. 1991, Hintz et al. 1991).

These methods also provide a better view into the genome (all the genes carried by a haploid germ cell) of the pathogen than earlier methods. For example, Jeng et al. (1991) showed that the size of the mitochondrial genome was 40% larger for the non-aggressive isolates than for the aggressive ones. The restriction site map of the mitochondrial genome which is a diagram portraying a linear array of sites on the DNA segment at which specific enzymes cleave the molecule, showed that the various isolate groups differed from each other by discrete length mutations in their mitochondrial genome (Hintz et al. 1991). Based on the above criteria and some physiological characters, Brasier (1991) separated the aggressive sub-group from the non-aggressive one by classifying the former as a new species, which he named O. novo-ulmi, while the non-aggressive group maintained the name O. ulmi. Further investigations by Jeng et al. (1996) showed that the DNA sequence of the ITS1 and ITS2 region of the ribosomal gene of the aggressive and non-aggressive group display high homology but differ between each other in one DNA base pair showing the close relatedness of the two groups. The ribosomal gene is a very important genetic marker. It is highly conserved, stable and shows little change over long time periods. However some of its regions (DNA stretches) such as those known as internal spacers (ITS) show some variation while others known as 18S, 5.8S, or 26-28S are very stable. Both are used for characterization of taxonomic units. Lately Brasier and Mehrotra (1995) described a third species belonging to the Ophiostoma group: O. himal-ulmi. This species has been found on U. wallichiana in the Himalayas and lead to the hypothesis that the DED may have its origin in this relatively narrow geographic region.

Methods of molecular biology such as RFLPs of mitochondrial DNA (mtDNA), nuclear DNA fingerprinting and RFLPs of the ribosomal DNA (rDNA) are very sensitive tools not only for strainal characterization but also for monitoring population dynamics. Studies of strains of O. ulmi population from Manitoba, southeastern Saskatchewan and northern Dakota show that these populations are composed of well defined fungal strains (Hintz et al. 1993, Hubbes 1992). This observation is based on the restriction site pattern of the mtDNA. Analysis of the nuclear DNA fingerprinting and rDNA reveal that the nuclear type of all isolates is that of the aggressive sub-group (O. novo-ulmi) (Hubbes 1992). Mitochondrial DNA in O. ulmi is inherited from the mother and the nuclear DNA from the father (unpublished results from our laboratory). This means those strains carrying non-aggressive mitochondrial types and aggressive nuclear types resulted from a cross between a non-aggressive mother (O. ulmi) and an aggressive father. Such strains have been reported for Manitoba (Hubbes 1992). Very recently Brasier et al.

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(1998) found similar strains in Europe. These observations are of great importance for the selection and breeding strategies which attempt to develop elms that in future can tolerate the disease like Siberian elms. It further indicates that under North American field conditions the number of strains is rather limited, a fact that has also been found by Brasier (1996). Changes in non-aggressive and aggressive subgroups within two populations of American elm in New England has also been reported by Houston (1991), a fact already known from Europe (Brasier 1991). The population of the non-aggressive subgroup is declining.

Furthermore, spore deficient strains of O. ulmi have been successfully isolated; these natural mutants lack the ability to produce conidiospores, blastospores, and ascospores. As a result of these mutants, O. ulmi is incapable of causing internal and external disease symptoms normally associated with DED (Richards et al. 1982, Richards, 1993, 1994, 1998). Spore production is of insturmental importance for the pathogen for transmittance by the elm bark beetle vector and rapid distribution within the elms vascular system. Understanding the mechanism(s) that block O. ulmi sporulation may be very helpful in developing methods of DED control.

Fungal metabolites as factors of virulence

Although the aggressiveness of O. ulmi strains was initially established by inoculation experiments, the basis of this ability has not yet been precisely determined. Knowing these factors precisely would allow effective DED control strategies including the development and selection of long term disease tolerant American elms. Brasier and Gibbs (1976) have shown in crossing and subsequent inoculation experiments, that the F1 generation of the fungus does not exceed the virulence of their parents. Assumptions (based on circumstantial evidence) have been made that toxins, such as cerato ulmin (CU) (Takai 1980, Richards 1993), peptidorhamno-mannan (Claydon et al. 1980, Nordin and Storbel 1981, Scheffer 1983, Scheffer et al. 1987), glycopeptides and glycoprotein elicitors (Yang et al. 1989, Hubbes 1993) may function as factors of virulence. Binz and Canevascini (1996) stated that production of extra-cellular laccase may be important for the survival of the fungus in its host. Confirmation of these compounds as factors of virulence is still waiting. For example, experiments by Bernier (1988) did not confirm previous results by Takai (1980) showing a correlation between high CU production and virulence. It appeared that the only way to prove the role of CU as a key factor of virulence would be the production of a number of mutants that are unable to produce the CU toxin. These CU negative mutants (CU-) should not be able to cause DED when inoculated into elms. If they do, then CU is not a major virulence factor.

Bernier (1988) produced a large number of chemical induced mutants, but none were CU-. The problem with chemically induced mutants is that the fungal genome may be altered at many more sites than those phenotypically visible. This led to efforts to identify and isolate the genes responsible for CU production (Yaguchi et

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al. 1993, Bowden et al. 1994, Jeng et al. 1996). Once the CU gene had been isolated a CU- mutant was created by transformation-mediated gene disruption of an aggressive strain (O. novo-ulmi). Bioassay of the CU- strain in highly susceptible elm trees indicated no difference in percent of brown streaks under the bark and percent foliar wilting. Simultaneously Tegli and Scala (1996) obtained five CU- mutants by UV-irradiation. In their inoculation experiments two out of the five mutants showed significant reduction in pathogenicity when compared to the wild type. However, very likely the UV-treatment affected not only genes of the CU pathway but also a number of other genes sitting at important metabolic switching points not detected by the authors.

CU- strains do occur naturally and are pathogenic (Brasier et al. 1994). This would support the view that CU is not a major virulence factor. However there exists another possibility, i.e., that the gene(s) for pathogen virulence and CU production are located close to each other giving the impression of one single unit. The loss of one during reproduction or by mutation would not affect the expression of the other. Recent studies by Scala et al. (1997) found higher CU levels in wilting leaves of elm seedling infected with aggressive isolates (O. novo-ulmi) than in those leaves of seedlings infected with non-aggressive strains (O. ulmi). Temple (1997) found that a transformed non-aggressive strain, which over expresses CU production showed no alteration in virulence when compared to the parent strain. Unfortunately no experiments were conducted to test whether the CU gene of the aggressive strain was expressing the correct CU protein in vivo, as tested by Scala et al (1997). CU research is complicated with various conflicting results being obtained by different scientists. CU may one day be shown to be a major factor in pathogen fitness and virulence.

Virus-like RNA elements for the control of DED

In the mean time (Brasier 1983, 1986, Hoch et al. 1985, Rogers et al. 1986, Brasier et al. 1993, Webber 1987, 1993) described the occurrence of double stranded ribosomal nucleic acid (dsRNA) particles in isolates of the aggressive strains (O. novo ulmi) and non-aggressive strains, and termed them as d-factors. One of them, the d2 factor, has been associated with reduced vigor in infected isolates (Hong et al. 1998). Work in Brasier’s laboratory has been conducted to use the d-factor to control Dutch elm disease on a wide scale (Sutherland and Brasier 1997). The problem up to now has been that the d-factor is not easily transmitted from strain to strain, because not all strains are vegetatively compatible. Furthermore, the transformation of the fungus into the yeast phase, one of the main distribution phases of the fungus within the tree (Banfield 1941, Pomerleau and Mehran 1966, Pomerleau 1968) allows Ophiostoma individuals to lose deleterious d-factors (Webber 1993). Similar problems have been encountered in the US with hypovirulent strains of Cryphonectria parasitica, the causal agent of chestnut blight (Choi and Nuss 1992, Enebak et al. 1994). However recent investigations suggest that it is the effect of induced resistance triggered by the hypovirulent strain that is responsible for the survival of chestnuts infected by chestnut blight (Schafleitner and Wilhelm 1997, Ghabrial 1998).

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Apparently the transformation of virulent strains to hypo-virulent strains induces some changes in the physiology of hypo-virulent strains that affect the pathogen and mobilize effective defense reactions in the chestnut host.

Induced resistance for DED control

Our efforts here in Toronto concentrated on the defense mechanisms of elms in response to fungal infection. Cross-protection against aggressive strains of O. ulmi was reported in U. hollandica and U. americana (Scheffer et al. 1980, Hubbes and Jeng 1981). Seedlings of U. americana were indeed protected against the attack by aggressive strains when first inoculated with non-aggressive strains (Jeng et al. 1983, Duchesne 1985, Duchesne et al. 1986, Sutherland et al. 1995). We have isolated and identified a number of chemicals produced by the elm in response to the inoculations as mansonones A, C, D, E, F and G from fungal inhibitory sapwood extract of elm seedlings treated with O. ulmi (Dumas et al. 1983, 1986 Jeng et al. 1983). Procter and Smalley (1988) also observed increased mansonone accumulation in elm inoculated with O. ulmi strains. Wu et al. (1989) demonstrated the toxic effect of these chemicals on the physiology and ultra-structure of the fungus. Mansonones were first reported to accumulate in elms infected with O. ulmi by Elgersma and Overeem (1971). However, these authors were unable to correlate mansonone accumulation with resistance to DED. There are several reasons why these authors overlooked the correlation. For example they compared mansonone content between treatments on the basis of number of cuttings that were extracted rather than using a more precise unit of comparison such as dry or fresh weight. Smalley et al. (1993) and Procter et al. (1994), using a number of chemically induced mutants showing lower mansonone tolerance than the parent strains, point out that mansonones alone do not play a major role in the resistance of elms to DED. These authors could not correlate mansonone sensitivity of a number of DED fungal mutants with high virulence. This is not surprising since chemically induced mutants often are altered at many more loci (position that a gene occupies in a chromosome) than those tested and visible. Therefore correct interpretation of the results is very difficult without knowing all the affected loci and their genetic stability.

Nevertheless, mansonone production is a very sensitive and precisely measurable process implicated in the host’s reaction in response to pathogen invasion. It is definitely a part of genetically programmed sequences of host defense mechanisms in DED. Duchesne (1993) concluded that timing of expression of different mechanisms of resistance to DED is critical for both anatomical and chemical means of defense to be effective in localizing the pathogen. He bases his assumption on the faster accumulation of mansonones in U. pumila (Duchesne et al. 1985), the faster mansonone accumulation in U. americana inoculated with aggressive isolates, and finally on the faster barrier zone formation (Shigo and Tippet 1981) in non-host trees than in host trees inoculated with O. ulmi (Rioux and Ouellette 1991a, b). To isolate the mansonone-inducing factor of the DED fungus, a sensitive bioassay had to be developed. Szczegola-Derkacz (1988) showed that tissue cultures responded to O. ulmi inoculations with mansonone

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production. Autoclaved spores of the yeast phase of the DED fungus produced the same effect as living spores indicating that the compounds triggering mansonone production are heat stable. Yang et al. (1989) demonstrated that fungal culture filtrates, cytoplasm and cell walls of O. ulmi contain molecules that elicit mansonone accumulation in elm calli. The culture filtrate elicitor has been purified (Yang 1991) and its structure identified (Hubbes et al. unpublished results).

When elm seedlings and elm trees (10 cm in diameter) were first injected with the elicitor and then challenged with 8,000 to 1 million spores of an aggressive strain per tree, the treated trees showed significant difference in wilting when compared to the control. The 5-year old seedlings obtained the high spore dose, while the trees obtained the lower dose (unpublished results). A United States patent application based on the structure of the elicitor for the control of DED has been filed. The elicitor can be injected in liquid form or in pellet form into the tree. It is heat stable, has an indefinite shelf life, appears environmentally safe and easy to administer into the tree, particularly in pellet form. Field trials on the feasibility of pellet treatment as well as elicitor activity have been conducted in 1997 by a number of cities in Manitoba, Saskatchewan and Alberta. Field trials on the efficacy of the elicitor are presently being repeated in Ontario, Saskatchewan and Alberta. Investigations in our Forest Pathology laboratory on the mechanisms of induced resistance show that they follow similar complex defense reactions as those found in agricultural crops (Somssich and Hahlbrock 1998). The elicitor induces a chain of defense reactions that prevent the rapid spread of the fungus. However the difference between agricultural crops and elm trees is that elm trees are wild type individuals with greater genetic variability and therefore show greater variations in their defense reactions. Hence, control of fungal pathogens in trees by induced resistance is a new approach of disease control and appears to be one of the few remaining options to protect the existing elm populations in our communities against DED.

Since the first appearance of DED a nagging question has emerged over and over: “Is the elm tree worth saving, and will this tree follow the doomed fate of the North American sweet chestnut? The chestnut has lost its once vast territories and other tree species have taken its place. Why then worry about losing another native tree species?” The very emotional argument against such a statement is that although the North American continent is rich in number, variety and magnificence of native trees, no tree can replace the American elm in the hearts of the people. The argument goes further in that the elm typifies, as no other tree does, the finest things in North American life. No substitute greenery, however luxurious, could hide the scars that would be left by the loss of the elm in our cities.

Acknowledgements

Part of our work has been supported by NSERC, City of Winnipeg, Province of Manitoba, Province of Saskatchewan, Coalition to Save the Elms, University of

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Toronto. Many thanks also to Mike Allen, Chief Forester of the City of Winnipeg, for reviewing the manuscript.

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Pomerleau, R. 1968. Progression et localisation de l'infection par le Ceratocystis ulmi dans l'orme d'Amérique. Phytopath. Z. 63:301-327.

Pomerleau, R. 1981. Dutch elm disease in Canada. p. 8-9. In: Compendium of elm diseases (Eds. R.J. Stipes and R.J. Campana). Am. Phytopathol. Soc. St. Paul, MN.

Pomerleau, R. and R. Mehran. 1966. Distribution of spores of Ceratocystis ulmi labelled with phosphorus-32 in green shoots and leaves of Ulmus americana. Naturaliste Can. 93:577-582.

Procter, R.H. and E.B. Smalley. 1988. Localized accumulation of mansonones E and F in elms following inoculations with Ophiostoma ulmi. Can. J. Plant Pathol. 10:371 (Abstract).

Proctor, R.H., R.P. Guries and E.B. Smalley. 1994. Lack of association between tolerance to the elm phytoalexin mansonone E and virulence in Ophiostoma novo-ulmi. Can. J. Bot. 72:1355-1364.

Prosser, T. 1998. One company’s success against Dutch elm disease. Tree Care Industry June 1998:60-64.

Richards, W.C. 1993. Cerato-ulmin: A unique wilt toxin of instrumental significance in the development of Dutch elm disease. p. 89-151. In: Dutch Elm Disease Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag, Berlin, New York.

Richards, W.C. 1994. Nonsporulation in the Dutch elm disease fungus, Ophiostoma ulmi: evidence for control by a single nuclear gene. Can. J. Bot. 72:461-467.

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Richards, W.C. 1998. Novel spore deficient mutants of the dimorphic fungal plant pathogen, Ophiostoma ulmi. Crop Health Unlimited Horizons. CPS/APS joint meeting, July 6-7/97. Winnipeg, Manitoba. Phytopathology 88: No 9 (Supplement), 1998 S113.

Richards, W.C., S. Takai, D. Lin, Y. Hiratsuka and S. Asina. 1982. An abnormal strain of Ceratocystis ulmi incapable of producing external symptoms of Dutch elm disease. Europ. J. For. Path. 12:193•202.

Rioux, D. and G.B. Ouellette. 1991a. Barrier zone formation in host and non-host trees inoculation with Ophiostoma ulmi. 1. Anatomy and Histochemistry. Can. J. Bot. 69:2055-2073.

Rioux, D. and G.B. Ouellette. 1991b. Barrier zone formation in host and non-host trees inoculation with Ophiostoma ulmi. 2. Ultrastructure. Can. J. Bot. 69:2074-2083.

Rogers, H.J., K.W. Buck and C.M. Brasier. 1986. Transmission of double-stranded RNA and a disease factor in Ophiostoma ulmi. Plant Pathol. 35:277-287.

Roy, D.N., J.R. Purdy and P. Ayyamperumal. 1980. Distribution of methyl benzimidazol-2-yl carbamate phosphate in elm: effects of chemical properties and formulation variables. Can. J. For. Res. 10:143-151.

Roy, D.N., J.R. Purdy, P.A. Perumal and J.K. Grace. 1988. Effect of application equipment on the distribution of chlorpyrifos applied for Dutch elm disease vector control. Proc. Entomo. Soc. Ont. 119:63-68.

Scala, A., M. Pattuelli, L. Coppola, M. Guastini, S. Tegli, G. DelSorbo, L. Mittempergher and F. Scala. 1997. Dutch elm disease progression and quantitative determination of cerato-ulmin in leaves, stems and branches of elms inoculated with Ophiostoma novo-ulmi and O. ulmi. Physiol. Mol. Plant Pathol. 50:349-360.

Schafleitner, R. and E. Wilhelm. 1997. Effect of virulent and hypovirulent Cryphonectria parasitica (Murr.) Barr on the intercellular pathogen related proteins and on total protein pattern of chestnut (Castanea sativa Mill.). Physiol. Mol. Plant Pathol. 51:323-332.

Scheffer, R.J. 1983. Toxins in Dutch elm disease. p. 82-85. In: Research on Dutch elm disease in Europe (Ed. D.A. Burekin). Forestry Commission Bull. 60, London.

Scheffer, R.J., H.M. Heybroek and D.M. Elgersma. 1980. Symptom expression in

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elms after inoculation with combinations of an aggressive and non-aggressive strain of Ophiostoma ulmi. Neth. J. Pl. Pathol. 86:315-317.

Scheffer, R.J., J.I. Liem and D.M. Elgersma. 1987. Production in vitro of phytotoxic compounds by non-aggressive and aggressive isolates of Ophiostoma ulmi, the Dutch elm disease pathogen. Physiol. Molec. Pl. Path. 30:321-325.

Scheffer, R.J., A.C. Brakenhoff, A. Kerkenaar and D.M. Elgersma. 1988. Control of Dutch elm disease by the sterol biosynthesis inhibitors fenpropimorph and fenpropidin. Neth. J. Pl. Path. 94:161-173.

Schreiber, L.R. 1993. An old problem; a new approach. p. 51-59. In: Dutch Elm Disease Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag, Berlin, New York.

Schreiber, L.R. and A.M. Townsend. 1976. Variability in aggressiveness, recovery and cultural characteristics of isolates of Ceratocystis ulmi. Phytopath. 66: 239•244.

Sherald, J. 1993. Demands and opportunities for selecting disease resistant elms. p. 60-68. In: Dutch Elm Disease Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag, Berlin, New York.

Shi, J.L. and C.M. Brasier. 1986. Experiments on the control of Dutch elm disease by injection of Pseudomonas species. Eur. J. For. Path. 16:280-292.

Shigo, A.L. and R. Campana. 1977. Discoloured and decayed wood associated with injection wounds in American elm. J. Arboric. 3:230-235.

Shigo. A.L. and J.T. Tippet. 1981. Compartmentalization of American elm tissues infected by Ceratocystis ulmi. Plant Disease 65:715-718.

Smalley, E.B. 1978. Control tactics in research and practices: IV. Systemic chemical treatments of trees for protection and therapy. p. 34-39. In: Dutch elm disease: perspectives after 60 years (Eds. W.A. Sinclair and R.J. Campana). Cornell Univ. Agric. Exp. Stn. Search (Agriculture) 8.

Smalley, E.B. and R.P. Guries. 1993. Breeding elms for resistance to Dutch elm disease. Annu. Rev. Phytopathol. 31:325-352.

Smalley, E.B., R.P. Guries and D.T. Lester. 1993. American liberty elms and beyond: going from the impossible to the difficult. p. 26-45. In: Dutch Elm Disease

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Research: Cellular and Molecular Approaches. (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag, Berlin, New York.

Smalley, E.B., K.F. Raffa, R.H. Proctor and K.D. Klepzig. 1993. Tree responses to infection by species of Ophiostoma and Ceratocystis. p. 207-218. In: Ceratocystis and Ophiostoma, Taxonomy, ecology, and pathogenicity (Eds. M.J. Wingfield, K.A. Seifert and J.F. Webber). APS, St. Paul, Minnesota.

Somssich, I.E. and K. Hahlbrock. 1998. Pathogen defence in plants - a paradigm of biological complexity. Trends Plant Sci. 3(3):86-90.

Stennes, M.A. and D.W. French. 1987. Distribution and retention of thiabendazoic hypophosphite and carbendazim phosphate injected into mature American elms. Phytopath. 77:707-712.

Sticklen, M.B., M.G. Bolyard, R.K. Hajela and L.C. Duchesne. 1991. Molecular and cellular aspects of Dutch elm disease. Phytoprotection 72:1-13.

Stipes R.J. and R.J. Campana. 1981. Compendium of elm disease. Amer. Phytopathol. Soc., St. Paul. MN.

Strobel, G.A. and D. Myers. 1982. Bacterial antagonism as a strategy for the treatment of Dutch elm disease. p. 46•61. In: Proceedings of the Dutch elm disease symposium and workshop, Winnipeg, Manitoba, October 5•9, 1981 (Eds. E.S. Kondo, Y. Hiratsuka and W.B.G. Denyer). Manitoba Department of Natural Resources, Manitoba, Canada.

Sutherland, M.L. and C.M. Brasier. 1997. A comparison of thirteen d-factors as potential biological control agents of Ophiostoma novo-ulmi. Plant Pathol. 46:680-693.

Sutherland , M.L., L. Mittempergher and C.M. Brasier. 1995. Control of Dutch elm disease by induced host resistance. Eur. J. For. Path. 25:307-318.

Szczegola-Derkacz, M. 1988. Induction of mansonones by Ophiostoma ulmi in tissue cultures of Ulmus americana and Ulmus pumila. M.Sc.F. thesis, Department of Forestry, University of Toronto.

Takai, S. 1980. Relationship of the production of the toxin, cerato•ulmin, to synnemata formation, pathogenicity, mycelial habit, and growth of Ceratocystis ulmi isolates. Can. J. Bot. 58: 658•662.

Tegli, S. and A. Scala. 1996. Isolation and characterization of non-cerato-ulmin producing laboratory induced mutants of Ophiostoma novo-ulmi. Mycol. Res. 100(6):661-668.

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Temple, B.O. 1997. The biological role of the hydrophobin cerato-ulmin in the life history of Ophiostoma ulmi and O. novo-ulmi. M.Sc.F. thesis, Department of Botany, University of Toronto. 133 pp.

Tomalak. M., H.E. Welch and T.D. Galloway. 1989. Nematode parasites of bark beetles (Scolytidae) in southern Manitoba, with descriptions of three new species of Sulphuretylenchus Rühm (Nematoda: Allantonematidae). Can. J. Zool. 67:2497-2505.

Townsend, A.M.and F.S. Santamour, Jr. 1993. Progress in the development of disease-resistant elms. p. 46-50. In: Dutch elm disease research: Cellular and molecular approaches (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag New York, Inc.

Ware, G. and F. Miller. 1997. Developing better elms. American Nurseryman August 15, 1997:44-51.

Webber, J.F. 1987. Influence of the d2 factor on survival and infection by the Dutch elm disease pathogen Ophiostoma ulmi. Plant Path. 36:531-538.

Webber, J.F. 1990. Relative effectiveness of Scolytus scolytus, S. multistriatus and S. kirschi as vectors of Dutch elm disease. Eur. J. For. Pathol. 20:184-192.

Webber, J.F. 1993. D factors and their potential for the control of Dutch elm disease. p. 322-332. In: Dutch elm disease research: Cellular and molecular approaches (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag New York, Inc.

Westwood, A.R. 1991. A cost between analysis of Manitoba’s integrated Dutch elm disease management program 1975-1990. Proc. Entomol. Soc. Manitoba 47:44-59.

White, J.C. 1982. An industrial approach to biological control of Dutch elm disease. p. 71•77. In: Proceedings of the Dutch elm disease symposium and workshop, Winnipeg, Manitoba, October 5•9, 1981 (Eds. E.S. Kondo, Y. Hiratsuka and W.B.G. Denyer). Manitoba Department of Natural Resources, Manitoba, Canada.

Wu, W.D., R.S. Jeng and M. Hubbes. 1989. Toxic effect of elm phytoalexin mansonones on Ophiostoma ulmi, the causal agent of Dutch elm disease. Europ. J. For. Path. 19:343-357.

Yaguchi, M., M. Pusztai-Carey, C. Roy, W.K. Surewicz, P.R. Carey, K.J. Stevenson, W.C. Richards and S. Takai. 1993. Amino acid sequence and

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spectroscopic studies of Dutch elm disease toxin, cerato-ulmin. p. 152-170. In: Dutch elm disease research: Cellular and molecular approaches (Eds. M.B. Sticklen and J.L. Sherald). Springer-Verlag New York, Inc.

Yang, D. 1991. Isolation, identification and characterization of phytoalexin elicitors from Ophiostoma ulmi. Ph.D. thesis, Department of Forestry, University of Toronto.

Yang, D., R.S. Jeng and M. Hubbes. 1989. Mansonone accumulation in elm callus induced by elicitors of Ophiostoma ulmi, and general properties of elicitors. Can. J. Bot. 67:3490-3497.

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Elmcare.com - American Elm

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American Elm Ulmus americana L.

Height 35m (115')

Leaves 10-15cm (4-6")

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The American or White elm is the largest species of elm. Due to its graceful form and size, it was an extremely popular urban tree before the spread of Dutch elm disease. Once found mostly in eastern North America, remaining populations of mature American elms are concentrated in the American Midwest and Canadian Prairies.

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Rock Elm Ulmus thomasii Sarg.

Height 25m (80 feet)

Leaves 5-10cm (2-4 inches)

This elm species, also known as the cork elm due to corky ridges on branches, is probably the least typical in form. Rather than branching out into large co-dominant limbs, the trunk remains distinct almost to the top of the tree. The crown is cylindrical in shape and can grow to approximately 25m in height. A relatively rare tree, it occurs mainly in the US Midwest. The leaves are 5-10 cm long and hairy on the underside.

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Slippery Elm Ulmus rubra Muehl.

Height 40m (132')

Leaves 15-20cm (6-8")

The Slippery or Red elm is rather uncommon and lives mainly in the eastern half of the US and southern Ontario and Quebec. The crown is umbrella-shaped with a high canopy and the leaves are quite rough to the touch.

Slippery elm is vulnerable to many of the same of the diseases as American elm including Dutch elm disease and, as a result, rarely reach full maturity.

This tree has also been an important component of herbal medicine for more than a century. Native Americans and early settlers used the dried inner portion of the bark to soothe irritated stomachs and to heal wounds.

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Scotch Elm Ulmus glabra Huds.

Height 40m (132')

Leaves 8-16cm (3-6")

Also known as Wych elm, these trees are native to Europe and western Asia and common in North and West Britain and Ireland. Similar to the Slippery elm, this tree is often planted in urban centers in eastern North America. Often growing to a height of 40m, 500 year-old specimens are known to exist.

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Elmcare.com - Camperdown Elm

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Camperdown ElmUlmus glabra camperdownii

Height 3-5 m (10-15 feet)

Leaves 8-18 cm (3-7 inches)

Also known as the Umbrella Elm or Weeping elm, this tree originated from a seedling at Camperdown House, near Dundee Scotland. It is in fact a cultivar of the Scotch elm.

The leaves show a high degree of asymmetry at the base and are dark green in colour. The drooping branches have made it attractive as a small-scale landscape tree.

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Elmcare.com - Siberian Elm

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Siberian Elm Ulmus pumila L.

Height 40m (132 feet)

Leaves 2-7cm (1-3 inches)

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This medium-sized tree is native to northeastern Asia, but has been extensively planted in cities across North America – especially in the West. This is due to the Siberian elm’s resistance to Dutch elm disease and other pathogens.

The Siberian is extremely drought resistant. In grows at altitudes of up to 3900m in Tibet and once grew in the Gobi desert. After the drought of the 1930’s in the US Midwest, Siberian elms were planted extensively and became the most widely planted shelterbelt tree in North America. It is now found in places as distant as the USSR and Argentina where arid land came under cultivation.

Thriving on moist soils, this hardy tree can flourish in adverse conditions. Leaves are narrow and between 2 and 7 cm long. Unlike other elm species, the leaves are almost symmetrical at the base. The bark is gray and rough.

Many arborists consider the Siberian elm an undesirable street tree due to its weak wood and prolific seeding.

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Elmcare.com - English Elm

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English Elm Ulmus procera Salis.

Height 40m (132 feet)

Leaves 8-16cm (3-6 inches)

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This elm was relatively rare until the 17th and 18th centuries when it was planted extensively by landowners along hedges that surrounded farmland. The leaves are 6-9 cm long with a rough upper surface, and hairy underside.

Selected for their shade cover, genetic variation was reduced making the species especially vulnerable to Dutch elm disease. After the disease reached Britain in 1967, more than 12 million English elms perished. Mature English elms can grow to 36m and have narrow crowns.

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Elmcare.com - Japanese Zelkova

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Japanese Zelkova Zelkova serrata Thunb. Mak.

Height 15-20 m (50-60 feet)

Leaves 3-5cm (1-2 inches)

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Native to Japan, this medium-sized tree has the vase-shaped form typical of American elms. Its tolerance of Dutch elm disease has made it a popular choice to replace disease-stricken populations. It flourishes in almost any good soil preferring a deep, well-drained moist loam.

Fast-growing, its leaves are slender and 3-5 cm long with 8-14 veins per side ending in a single sharp tooth.

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Elmcare.com - Winged Elm

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Winged ElmUlmus alata

Height 10-12 m (40-50 feet)

Leaves 4-8 cm (1.5 to 3 inches)

A small to medium-sized tree native to the southeastern U.S.

The bark is flat with scaly ridges separated by shallow, irregular furrows.

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Elmcare.com - Chinese Elm

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Chinese ElmUlmus parvifolia

Height 6-18 m (20-60 feet)

Leaves 2-7 cm (0.8 to 2.5 inches)

Native to northern China, Japan, and Korea, the Chinese or Lacebark elm generally has a broad, vase-like shape with pendulous branches. In warmer regions, it may be evergreen. The bark is usually smooth. It grows fairly quickly and is resistant to Dutch elm disease making it a popular choice for landscaping.

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Elms in Winnipeg - Part 1

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olseley Avenue wanders through a gentrified Winnipeg neighbourhood on the north side of the Assiniboine River, its 2.5 kilometres of sidewalk dappled by light that filters through a canopy of American elms.

Sometimes the shady street follows the meandering course of the muddy brown river; at other times, like Portage Avenue just to the north, it obeys the dictates of traffic engineers and straightens out. But whether straight or curvaceous, it is always lined with grand, old, century elms. Hundreds of them.

Back in the 1950s, when Winnipeggers began their passionate affair with the automobile, if you wanted to avoid busy Portage Avenue on your way downtown or if you lived in the south end and were on your way to see a Blue Bombers game at the new Winnipeg Stadium, Wolseley was a fast alternate route with no bothersome traffic lights or stop signs. It did, however, have an old tree growing smack-dab in the middle of the road near the corner of Basswood Place. The ancient Wolseley elm, according to local lore, was planted in 1859 by a girl named Mary Anne Good who lived on a prairie farm near the bank of the Assiniboine. Nearly 100 years later, by some road-planning oversight, it was still there, although surrounded by a curb and a fringe of grass that Ripley's Believe It Or Not declared was "the smallest park in the world." Motorists, however, were not amused, and city officials worried that someone might drive into it and kill themselves. Neighbourhood residents argued that the tree protected their kids from being killed by speeding cars.

In September 1957, at the height of the football season, the city assigned a crew to remove the offending elm. In the ensuing standoff, a dozen neighbourhood women circled the tree, arm in arm, to fend off the buzz saws, and within minutes the police had arrived, paddy wagons and all. A crowd gathered.

"If they want to chop down this tree," said one of the women, "they're going to have to chop us down first."

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Elms in Winnipeg - Part 1

In the end, the matter was settled peaceably by newly-elected mayor Stephen Juba, who pulled up in his Cadillac and sent the workers home. Most of the rest of the neighbourhood's trees have also survived, somehow evading both the urban-planners' axe and the more serious threat of Dutch Elm Disease. In fact, the city remains shaded by a forest comprised of over 200,000 elms, a remarkable legacy that is guarded by Winnipeggers every bit as vigilant as the defenders of the Wolseley Elm. Their appreciation of the urban forest, and their decades-long battle against a disease that has virtually extirpated the elm from the streets of most other cities, is now finally offering some hope for those who might otherwise have given up on what was once eastern North America's most popular city tree.At the turn of the century, when the grain and railroad boom was fuelling Winnipeg's growth, the city fathers looked south for inspiration and were, perhaps inevitably, inspired by Chicago, a city with a similar economy, monumental architecture, grand streets, and lots of elm trees. By then, much of eastern North America had been cleared of forest, and city dwellers were starting to rethink the value of trees. Arbour Day had become fashionable, and tree planters had only to look to adjacent farmsteads, where the stubborn Ulmus americana, a very tough tree for settlers to remove, still proliferated. The giant American elms that survived the agricultural clearances and thrived on prime farmland became the source of the graceful, parasol-shaped trees that would dominate the urban forests of North America for decades to come.

Part 1 Part 2 Part 3 Part 4

Jamie Swift is a writer and broadcaster living in Kingston, Ontario. His most recent book, Wheel of Fortune, was published in 1995. He is also the author of Cut and Run, a lament for the mismanagement of Canadian forests.

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Elms in Winnipeg - Part 2

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Winnipeg's early planners had a perfect source of planting stock at hand. When the time came to bring trees into the newly laid-out subdivisions on both sides of the Assiniboine and Red rivers, they simply collected native elms from the riverbanks. Each new city park featured a nursery where the trees were grown to sapling size before being transplanted along the generous boulevards. The city charged each homeowner a lot levy and planted an elm in front of every residence, and Winnipeg's splendid urban forest was born. It's

a democratic forest, lining not just the tonier streets of southern neighbourhoods but also offering shade and comfort to people in Winnipeg's storied north end, where successive waves of poor immigrants-most recently aboriginal people from reserves-have settled in the rundown streets around Selkirk Avenue.

"Our forest is unique in the world," enthuses chief forester Mike Allen as he surveys the elms that shade Palmerston Avenue in the Wolseley district. "There's no other city anywhere with this incredible natural arch of trees." A tall, thoughtful man with the image of a tree etched on his brass belt buckle, Allen grew up in Toronto at a time when the dreaded Dutch elm disease was obliterating the elm from the city's parks and lawns. "When I was eight," he says, "I noticed workers removing one giant after another along my route to school, and whenever I travelled around southern Ontario, I witnessed the death of elms standing like weird witch's broomsticks." He has vowed not to let that happen in Winnipeg. He points to a four-storey elm and describes the multipronged fight he has waged against Dutch elm disease, explaining that the trees' rough and diverse origins on the banks of the Assiniboine were the key to their survival. "They're not high-tech clones cultivated for certain desirable traits," he says. "They were selected purely from native stock, so they had tremendous genetic diversity even though they were all one species. Today, I can show you elm from all over Winnipeg, all American elm, but you might look at one and say, "That's not the bark of an American elm.' " As we tour the city's forest, it becomes clear that most Winnipeg elms have the elm's characteristic bark, deeply furrowed and light grey, like a heavy grade of rough corduroy. Some, however, have no fissures or ridges, and the bark is dark or tinged with brown. Sometimes the leaves are enormous; sometimes they're

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Elms in Winnipeg - Part 2

small. Some leaves have sawtooth edges and grow in double rows; sometimes the edges are wavy and the rows are triple. Such variation makes for a more resilient species, because certain variants seem to have an inherent resistance to Dutch elm disease. Not all of them, however. Five years ago, in the biggest single elm infection that Winnipeg has witnessed, the disease destroyed 20 mature elms at Palmerston and Ethelbert. The memory still makes Mike Allen shudder. But the resilient variants survived the infestation, and their genetic material may help save the species.

Dutch elm disease, so named because it was first identified in the Netherlands in 1917 or 1918, likely originated in Asia. It's an infection of the deadly fungus Ophiostoma ulmi, which enters and disrupts the tree's vascular system literally on the back of the elm bark beetle, Hylurgopinus rufipes. The scourge reached the United States in 1930, with the first Canadian outbreak reported in Sorel, Quebec, in 1945. Within a few years, more than 600,000 elms in Quebec had been wiped out. Toronto's population of 35,000 elms was quickly reduced by 80 percent. According to the University of Toronto's Martin Hubbes, a leading Dutch elm disease researcher, "one of the largest mass destructions of trees ever witnessed" accelerated when the Canadian and American disease fronts merged and began to migrate westward, travelling up the Red River from South Dakota into southern Manitoba in the early 1960s, most likely brought in by campers hauling infected firewood. The disease was reported in Winnipeg in 1975 and by 1990 was infecting elms in Saskatchewan. This year, it arrived in Alberta. Today, possession of elm firewood-infected or not-can bring a $5,000 fine in Winnipeg, where they take the threat seriously. Since the disease's arrival, some 34 percent of city elms have been infected and cut down.

It's a paradoxical story, at least as far as Winnipeg is concerned. The same riverbank forests that provided the city with its rich genetic diversity now offer an ideal host for Dutch elm disease. Because the Assiniboine, La Salle, and Seine rivers empty into the Red near Winnipeg, their rich silt valleys provide both a breeding ground and a highway for the elm beetle. The province has earmarked and sporadically protected a buffer zone surrounding Winnipeg. This is a crucial battlefield in the war to save the city's cherished elms. The idea is to remove infected trees from this zone in an attempt to protect the city proper. Other western cities that depend on the elm for shade, shelter, and beauty are luckier because they are more like isolated islands in the prairie, with little contiguous elm forest.

Another paradox. Despite the devastation of the urban elm forests of Toronto and Montreal, those central Canadian cities are well situated to bounce back. Their relatively moderate climates can support a wide variety of trees, from the colourful red maple to the elegant black walnut. Winnipeg's famously frigid winters mean that few species can thrive there. The American elm, one of the hardiest, is ideal. Not only sublimely beautiful, it's tough enough to resist road salt and devastating cold. What's more, Winnipeg's harsh winters have little appeal for the European elm bark beetle, Scolytus multistriatus, a larger, hairier critter that's a perfect host for the toxic fungus. As long as Winnipeg has only the native prairie variety, its elms have a fighting chance. Yet Mike Allen remains cautious.

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Elms in Winnipeg - Part 2

"Insects are highly versatile and opportunistic," he warns. "It may well only be a matter of time before we get European beetles reproducing themselves and becoming hardy enough to invade Manitoba."

Part 1 Part 2 Part 3 Part 4

Jamie Swift is a writer and broadcaster living in Kingston, Ontario. His most recent book, Wheel of Fortune, was published in 1995. He is also the author of Cut and Run, a lament for the

mismanagement of Canadian forests.

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Elms in Winnipeg - Part 3

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The past 20 years have witnessed widespread conflicts over ancient trees and old-growth forests. A familiar snapshot: Environmentalists cry foul, claiming the wilderness is being strip-mined. Loggers and millworkers cry foul, claiming their jobs are being jeopardized by a Birkenstock brigade of outsiders who return to comfortable condos once the camera crews depart. The conflict is, in a very real way, about a sense of place. Many environmentalists plead for places they cherish. That place, however, is often somewhere else: the boreal forest, the Pacific rainforest, the wilderness. For many Canadians, nature is, indeed, something out there in cottage

country, a wilderness park, a summer camp-a rural landscape, not a city streetscape.

When Mary Anne Good planted the Wolseley elm, most Manitobans were sod-busting settlers. Twenty years later, when landscape architect Frederick Law Olmsted urged Montrealers to make their new park on Mount Royal a naturalistic retreat ("You can put in a broad dark mass of low mountain pine, or pensive, feathery and brooding hemlock . . . to supply the degree of canopy and shadow which will be the most effective for your purpose"), Quebecers were still by and large country folk. We're about to enter the planet's first truly urban century: a majority of the world's people now live in cities, and although Canadians may visit a wilderness place from time to time, we pass our daily lives in the shadow of an urban forest.

Urban forest may sound like a contradiction in terms, but not to Judy Werier, the peppy director of Winnipeg's Coalition to Save the Elms. As we drive around trendy Osborne Village to check out the condition of its trees, she hits the brakes and jumps out of her car to rip a yard-sale sign off a sidewalk elm.

"Can you believe this?" she fumes, hurling the offending poster into the back seat. "It was nailed to the tree! Someone actually used four nails!"Jamming the car into gear, she mutters something about going over to the yard

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Elms in Winnipeg - Part 3

sale on Saturday to scold the culprit. She explains that nails provide another way into the tree for the elm bark beetle and wood-boring beetles and hence for the fungus that causes Dutch elm disease. Heading along River Avenue, she has trouble keeping her eyes on the road as she points out the cankerworm bands that residents have dutifully wrapped around their neighbourhood trees, scolds construction foremen for neglecting to strap protective lumber around trees on building sites, and of course, keeps an eye out for the telltale flagging that indicates an elm has been infected.

Citizen involvement has been crucial to Winnipeg's efforts to preserve the elm forest. Coalition members report "hazard" elms to Mike Allen's department, where every summer forestry staff adopt a war-room approach, sticking hundreds of red and black pins onto a map as they chart sightings of the disease. There are lots of pins along the rivers. The city uses an expensive fungicide injection system on valuable park trees, while a less expensive basal spraying technique is aimed at zapping beetles with an insecticide containing chlorpyrifos. This prevents the beetles from overwintering in the tree but must be done annually. The principal defence, however, is sanitation, which includes tree removal and pruning of dead branches: some diseased trees can be saved by fungicidal injection, but many are simply cut down. It's a $2 million-a-year battle, but Werier thinks it's worth it. Aside from organizing workshops on tree planting, identification, pruning, and Dutch elm disease, the coalition helped pressure the province into restoring some of the $3 million it had cut from the program to control the spread of the disease in the buffer zone around the city.

"My husband calls me 'a crazy militant little person,' " she says as we head out Portage Avenue. When I ask her about her commitment to the urban forest, why she's such a tree zealot, she responds in the same way a wilderness tree hugger might. "I love the trees," she says after a moment's thought. "That's all I can say. There are no words I can put to it. It's emotional."

Werier got an early start in urban forestry. Her father, Val Werier, a longtime Winnipeg newspaper columnist who recently won the Order of Canada for his advocacy work, used to quiz her about trees, teaching her to tell an ash from an elm. "When Dad came home from work, we'd go for a brisk walk. I'd have to run to keep up with him, but he taught me about trees, and I developed a real appreciation for them. So when I became involved with the elms, I said to myself, 'This feels right.' "

In 1969, Val Werier was pushing for a bylaw to control the removal of trees on public land. Three years later, he was telling his readers to get out and put sticky bands on elms to protect them from cankerworms. And in 1974, the year before Dutch elm disease was first identified in Winnipeg, he wrote a long series of columns on the imminent threat. By 1976, he was writing that government action wasn't enough-Winnipeggers had to get involved in the fight against the disease. Werier was soon able to point out that Manitoba was the first North American

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Elms in Winnipeg - Part 3

jurisdiction to require the removal of diseased elms from private and public property.

"There's a history of citizen activism here," Mayor Glen Murray told me when I asked him about Werier. "And a very practical reason is that the absence of the elms would have a huge negative impact on property values and the enjoyability and livability of neighbourhoods."

A city forest has a long list of virtues. Urban air, full of carbon dioxide and a host of noxious car fumes, is measurably improved in cities where a dense overstorey of trees adds life-giving oxygen. The forest moderates storm runoff. A deciduous forest protects houses from the summer heat, saving on air-conditioning costs while permitting passive solar gain in wintertime. If it's dense enough-as it is in Winnipeg-it acts as a winter windbreak. It also buffers the ceaseless white noise of city traffic. Parents can take comfort that shaded play areas are safe in an era when high-ultraviolet sunlight is cause for concern. Realtors know that a treelined street is a price-boosting part of their "location, location" mantra.

Though she has a passionate attachment to the urban forest, Werier inherited a lobbyist's understanding of how to protect it. She knows that she can't just rely on the virtues of nature appreciation when it comes to navigating the political terrain at city hall. A savvy politician, Glen Murray is well aware that Stephen Juba, Winnipeg's longest-serving mayor, made an early and lasting impression when he defended the Wolseley elm in 1957. "If you ever want to lose elected office in Winnipeg," says the mayor wryly, "say something bad about a tree."

Of course, all the political will in the world will not stop the steady onslaught of Ophiostoma ulmi. That's why Winnipeg, prodded by Werier and the Coalition to Save the Elms, has been sending cheques to the Faculty of Forestry at the University of Toronto, where Martin Hubbes and his research team have recently developed a vaccine that immunizes the elm against the fungus. With patents on the way, Canadian scientists have helped spark renewed international interest in a problem that many had given up as a lost cause.

Part 1 Part 2 Part 3 Part 4

Jamie Swift is a writer and broadcaster living in Kingston, Ontario. His most recent book, Wheel of Fortune, was published in 1995. He is also the author of Cut and Run, a lament for the

mismanagement of Canadian forests.

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Elms in Winnipeg - Part 4

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Hubbes began studying Dutch elm disease in 1968 and quickly became fascinated by the many ways trees react to the threat of infection. When bark beetles laden with fungal spores burrow their way under the craggy bark of an elm, the tree responds to the invasion with what Hubbes describes as a

"cascade of defensive reactions," including the production of compounds called mansonones that help ward off fungal infestation. He and his colleagues have succeeded in isolating from the fungus a glycoprotein "elicitor" that tricks the tree into mounting its protective cascade.

"What the tree tries to do," explains Hubbes, "is to wall the fungus off in a confined space so that it cannot further invade the vascular system. The trees actually shut down the cell walls and surround the fungus with an inert tissue so that the fungus cannot penetrate the tree further."

Once the defences are elicited and the fungus is isolated, the host tree is then primed with antifungal mansonones (related to a group of substances called sesquiterpine quinones) that destroy the fungus. "They kill by attacking mitochondria, the energy powerhouses of the fungus," Hubbes told New Scientist magazine last year after news of the discoveries began to filter out. Since then, there's been a surge of international attention. "It was incredible how a much renewed interest flared up around the world," Hubbes says now in his Toronto lab. A plant pathologist who seems torn between modesty ("We didn't want a lot of propaganda because we like to work in a quiet atmosphere") and bubbling enthusiasm for saving trees, he can't help letting the enthusiasm surface. "We're getting inquiries from all over the world," he says, "the U.S., Australia, New Zealand, Europe." Everyone, its seems, wants their elms back.

Hubbes and his colleagues are busy conducting field tests in Winnipeg, Toronto, and several other places in Ontario, treating trees with the elicitor and then exposing them to high dosages of Ophiostoma ulmi spores "to see how good the stuff is." They have also begun to treat elms in Saskatchewan and Alberta but

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Elms in Winnipeg - Part 4

have carefully avoided introducing any fungus to vulnerable stands of elms there. Results are already encouraging. In one trial, all the trees in the control group died when exposed to the fungus, whereas only one in 33 vaccinated trees succumbed.

Hubbes agrees that Winnipeg has a natural advantage because of its genetically diverse elm population. But here again, Canada's richest urban elm forest presents paradoxical problems inherent in any effort to intervene with a complex ecological system.

"For our treatment, wide diversity within the species is not so good," Hubbes says. "If I could just treat clones of a single variant, it would be so much easier for me because one cloned tree would react the same as a thousand others. But where there's high diversity, some trees do very well, while others require more conditioning."

Another variable is the influence of the tree's environment. A handsome old elm standing alone on a rural fence row may survive because it's being nourished by good agricultural soils. "When you plant them in a city where you have a dreadful environment," says Hubbes, "they might not react the same way. That's why we have to understand the defence mechanisms. Once we do that, then I think we'll have solved the problem."

Hubbes admits that even after 30 years of study, there's still much to learn about the immune systems of Ulmus americana, particularly in a forest ecology as complex as that of Winnipeg. But he is in no doubt about the prairie city's role in sustaining the work that finally seems to be bearing fruit. "If Winnipeg hadn't supported us," he says, "I would have given up a long time ago." Most people, including Ottawa politicians and officials who have stopped supporting Dutch elm disease research, still hear the word elm and immediately think of those skeletal remains that dot the rural landscape in eastern Canada. Hubbes keeps getting advice from people who say, "The elm? Don't bother. It's dead, forget about it."

But it's not dead in Winnipeg. "I grew up in Montreal when all of the elms died and the city didn't act to save them," recalls Glen Murray. "I remember very vividly the trees disappearing in my neighbourhood. Here in Winnipeg, people have a real attachment to the trees. It's part of our identity as a city." And thanks to officials like Mike Allen and citizen activists like Judy Werier, tree huggers whose stubbornness was perhaps inherited from the women in the cloth coats who defended the Wolseley elm, eastern cities may one day rejoice again under their own restorative canopies of stately elms.

Part 1 Part 2 Part 3 Part 4

Jamie Swift is a writer and broadcaster living in Kingston, Ontario. His most recent book, Wheel of

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Elms in Winnipeg - Part 4

Fortune, was published in 1995. He is also the author of Cut and Run, a lament for the

mismanagement of Canadian forests.

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