Weed Control and Management

INAG 116 / ANSC 110February 19, 2008

Why Should I Worry? 1 Acre Weed Free Pasture/Horse = 40% to

60% of Yearly Feed Bill.

2 Acres Weed Free Pasture/Horse = 90% of Yearly Feed Bill (Haying Required)

Feed Ration is Unknown When Weedy

Some Weeds are Poisonous or Noxious

Weeds Reduce the Quality & Value of Hay

Weed Overview Interfere with forage establishment, yield,

and quality Compete for resources:

Light Space Nutrients Water

Weeds are indicators of deficiencies in a forage management program

Weed Overview Classified based on life span, season of

growth and method of reproduction

1. Annuals – Complete life cycle in one year and germinates in

spring or summer

2. Biennial – Complete life cycle in two consecutive growing

seasons and germinates in late summer or early fall

3. Perennials – Persist for more than 2 years and reproduce from

seed or asexually

Weed Overview Designations:

Native – part of North America plant communities before Europeans colonized the continent

Invasive – exotic species that pose a special threat because they lack natural enemies to limit population growth

Noxious – weeds that are regulated by law

Weed Management To plan an effective weed management

program, a producer must be able to identify weeds and understand how weed biology and ecology affects where weeds are found and their value or detriment.

Weed control decisions are based largely on visual thresholds and intuition.

Begins long before crop establishment.

Weed Management Some things to consider…

New establishment? Established pasture?

Management strategy

Incremental goal-setting

Where to start? Pasture-invading weed species should be

assessed for: Competitive ability – potential to reduce

desirable forage species Invasiveness – potential to multiply and

increase Yield quality – nutritive value relative to

desirable forage species Cost and effectiveness of control measures –

cultural, mechanical and chemical

Causes of an Unprofitable Pasture Overstocking

Cutting Strategies

Climate

Fertility and pH

Pest Control

Weed Management Strategies Prevention

removing weed seed and vegetative material from farming implements before preparing a seedbed for forage grasses

Planting seed that is not contaminated with weed seed

Control process of minimizing weed interference with

desirable plants to meet economic and production goals

Weed Management Strategies Eradication

complete elimination of weed requires removal of living plants and

destruction of seed in the soil

Early detection followed by swift, intensive and aggressive effective control measures during early invasion are essential to eliminate the invader.

Weed Control Measures

1) Cultural

2) Mechanical

3) Chemical

4) Biological

Cultural Control Includes anything that makes a crop more

competitive against weeds Focuses on improving the “health” of native

plants Practices include:

Fire Grazing Haying Revegetation or reseeding Plant competition Liming Fertilizing

Cultural Control – Things to consider… Consider seedbed preparation, planting

date, fertilization, planting population, and high-quality crop seed and select adapted species and varieties

Prevention is the most important tool for managing weeds on established pastures

Managing a dense, competitive forage is key to preventing weed invasion and interference

Cultural Control – Things to consider… Overseed in open areas

Test soils & fertilize annually

Rotational grazing systems

Prevent dispersal of seeds

Cultural Control - Fire Useful and essential practice to meet land

management objectives Used to control woody plants Can help increase nutritive value of

dominant grasses Increase grass seed production

Transition Pasture SystemsAnnual Forages

Renovate and reseed pastures until pasture problems are solved.

Use annual forages to correct or overcome pasture deficiencies or failures.

Use annual forages to develop successful perennial pastures.

Mechanical Control Involves either removal of the aerial

portions of the weed or removal of enough of the root and crown to kill the plant

Practices include: Tilling Mowing Removal by hand

Mechanical Control – Things to consider… Repeated mowing can:

reduce competitive ability deplete root carbohydrates prevent seed production

Mow at a height above grass seedlings when weeds are 8 to 10 inches tall to reduce shading

Mechanical Control – Things to consider… If you see a new weed, dig it, pull it, or

remove the seedhead before seeds can disperse

Mowing can kill or suppress annual and biennial weeds

High cost of these more energy intensive treatments limits their widespread use

Chemical Control Herbicides provide a convenient,

economical and effective way to help manage weeds

Allow fields to be planted with: Less tillage Earlier planting dates Additional time to perform the other tasks that

farm or personal life require Spot spraying is most economical

alternative for scattered infestations of weeds

Biological Control Release of organisms that attack plants to

control weeds

Aim is to shift the balance of competition between the weed and the crop in favor of the crop and against the weeds

Historically insects and mites have been most important

Biological Control Tools currently utilized:

Insects Mites Nematodes Pathogens Grazing Animals

Can be cost effective, environmental safe, self-perpetuating, and well suited to an integrated weed management program

Biological Control Strategies Conservation

involves manipulation of the environment to enhance the effect of existing natural enemies

usually used to manage native weeds

Augmentation employs periodic release of natural enemies restricted to managing weeds in high-value

food crops

Biological Control Importation

known as “classical” biological control the planned relocation of natural enemies of

exotic weeds from their native habitats onto weeds in their naturalized habitats

seeks to reestablish weed and natural enemy interactions that reduce the weed population to an acceptable level in the new environment

Beneficial Insects…Canada Thistle

Beneficial Insects…

Grazing Animals Can be used to minimize the spread of

certain weeds and to control large infestations

Does not completely eradicate weeds Common animals:

Cattle Sheep Goats* Horses

Biological Control…

Biological Control – Limitations Success in the past 200 years has been

variable

Hard to control alone due to environmental changes

Although slow in coming, it may have a major impact on managing problem weeds in pasture systems in the future

Integrative Management A program that combines cultural,

mechanical, chemical, and perhaps biological tools

Can provide a effective economical weed management program in pasture systems

Prevention is the most important consideration for managing weeds in established pasture systems

Adaptive Management Complements integrated programs Requires manager to:

Establish management goals Develop and implement management

programs based on goals Monitor and assess impacts of management

efforts Modify goals and invasive plant management

in light of new information