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Dalmatian Toadflax

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Abstract

Dalmatian toadflax is an escaped herbaceous perennial, with an extensive creeping root system and bright yellow and orange flowers.

Dalmatian toadflax’s flowers make it distinguishable from other invasive weeds as its showy flowers are grouped towards the end of their stems and possess a spur resembling a snapdragon flower.

Two forms of Dalmatian toadflax are found in the United States: Narrowleaf and Broadleaf Dalmatian toadflax, with both forms able to hybridize.

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AbstractDalmatian toadflax was originally native to the Mediterranean region of

the world; and was first reported being grown as an ornamental in North America in the late 1800s.

Since its initial escape, Dalmatian toadflax has spread throughout the North America, with the worst infestations occurring in the western United States and Canada.

Dalmatian toadflax reproduces by seed and by underground rootstalks. Dalmatian toadflax is considered a pest as it can significantly reduce crop yields, desirable livestock forage, and out-compete native and sensitive plant communities.

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Taxonomic ClassificationFamily

Dalmatian toadflax is a member of Scrophulariaceae, the Snapdragon or Figwort family. The Snapdragon or Figwort family is a group of 220 genera containing about 3,000 species of herbs, shrubs, and small trees.

Species in the figwort family include Penstemen, Monkeyflower, Mimulus, Snapdragon, and foxglove.

Some figworts, such as Monkeyflower, are edible. The drug digitalis,used for heart ailments, comes from a kind of foxglove. Yellow toadflax was used as a source for fabric dye. Scrophularia, from which the family name comes from, is a medicinal figwort. People at one time believed that Scrophularia could cure Tuberculosis.

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Taxonomic ClassificationGenus

Linaria, a generic name derived from the Latin linon or linum meaning flax. There are about 130 species in the genus Linaria, most being native to Eurasia.

Species

Linaria genistifolia (L.) P. Miller ssp. dalmatica (L.) Maire & Petitmengin. Although two varieties are found in North America, Broadleaf toadflax has a wider distribution.

Common Names

Common other names for Dalmatian toadflax are Broadleaf toadflax and Wild Snapdragon.

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Description

Dalmatian toadflax is an aggressive, highly competitive noxious weed that was introduced into North America as an ornamental, but was also used for fabric dyes, and folk remedies.

It soon escaped from host gardens invading farmland, pastures, and rangeland across North America, disrupting native plant communities, livestock forage, and wildlife habitat.

Dalmatian toadflax continues to be sold commercially as an ornamental plant, and is recommended for xeric landscape planting. However, Dalmatian toadflax can thrive in a wide range of habitats and climates and is difficult to eradicate.

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Description

A mature Dalmatian toadflax plant can contain many vertical floral stems reaching up to four feet in height. These stems, which are robust and woody at the base, are composed of thick- walled, fibrous xylem.

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Description

The flowers of Dalmatian toadflax, which reside towards the apical end of each stem, near the base of the leaves, are bright yellow with orange throats each possessing a spur, resembling a snapdragon.

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Description

Leaves of Dalmatian toadflax are light green in color, heart-shaped, pointed, waxy to the touch, and clasp closely to the stem.

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Description

Its taproot may penetrate up to 10 feet into the soil, with its lateral roots extending several meters. Dalmatian toadflax lateral roots develop adventitious buds that can develop independent plants.

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Life Cycle

General

Dalmatian toadflax can reproduce either by seed or vegetative propagation and can live up to 5 years.

Once a colony is established Dalmatian toadflax's high seed production and ability to reproduce vegetatively allows it to spread rapidly, making it highly resistant to eradication.

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Life CycleSeed Reproduction

Dalmatian toadflax usually begins flowering in June, continuing until September or October.

As plants are self-incompatible and cannot pollinate themselves, bumblebees and halictid (mining) bees are the primary pollinators.

Seeds are produced for about three months, starting late June or early July, lasting until early September. During this time, a Dalmatian toadflax plant can produce up to 500,000 seed, which can remain dormant for up to ten years.

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Life Cycle

Seed Reproduction

Seed dispersal begins in July and can continue into the winter and following year. Dalmatian toadflax seeds are small and angular with a small, irregular wing.

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Life CycleSeed Reproduction

Although wind is consider as the means of seed dispersal, other studies have indicated that 90% of the seeds fell within 2.5 feet of the plant.

Seedlings generally germinate in the spring; with a primary stem and one to three adventitious stems.

Emergent seedlings are quite vulnerable, with survival depending on little competition from other plants for soil moisture.

Adventitious shoots generated from rootstock are very competitive for soil moisture. It is this feature that allows Dalmatian toadflax to out-compete native plant communities.

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Life CycleAdventitious Reproduction

Dalmatian toadflax reproduces vegetatively. The above ground portion of the plant dies back in the fall. In spring, erect shoots begin growing from the root and may produce one to 25 floral stems.

These stems develop from adventitious buds on primary and lateral roots. Adventitious growth is possible from root fragments as short as 1 cm in length.

These buds then grow their own root and shoot systems, and become independent plants. Vegetative propagation can allow a stand of toadflax to spread rapidly.

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Distribution

Origins

Dalmatian toadflax was originally native to the Mediterranean region of the world. Its original range spanned from the coast of Croatia northeastward to the Romanian regions of Transylvania and Moldavia; and to the south and east around the Black Sea into the countries of Bulgaria, Albania, Greece, Crete, Turkey, Syria, Iran, and Iraq

In its region of origin, Dalmatian toadflax evolved in plant communities that were grazed by herbivores. Because much of the arable lands were aridic in its region of origin, Dalmatian Toadflax has adapted to dryness and periodic disturbances caused by agriculture.

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Distribution

Dispersal

The first known occurrence of Dalmatian toadflax in the United States was in 1874. Dalmatian toadflax has since spread throughout the United States. The worst infested states being in the west.

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Distribution

Dispersal

In California, Dalmatian toadflax is found almost in all of its counties with the exception of Amador, Fresno, Imperial, Kings, Marin, Mariposa, Orange, Riverside, San Benito, Santa Clara, Santa Cruz, Stanislaus, Sonoma, Sutter, Tuolumne, and Yuba.

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Distribution

Dispersal

In Butte County, a Dalmatian toadflax infestation took place in and around the Town of Paradise. The infestation was thought to haveinitially come from an escaped ornamental. Most Paradise sites were located along roadsides and in residents’ front yards.

As Dalmatian toadflax is classified as a Class-A noxious weed in the state of California, the outbreak needed to be completely eradicated.

The infestation was eradicated through handpulling and application or Tordon (Picloram) over a period of 5 years. As of 5/8/92 there has not been any reoccurrence of Dalmatian toadflax in Paradise.

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Distribution

Dispersal

Once mapped, it was clear that the majority of the infestations had south-facing aspect.

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Habitat

Dalmatian toadflax generally grows in open, sunny places, up to elevations of 9,000 feet and has a north/south latitudinal range between 330 and 560 degrees. Aspect is also implicated as it also to be found on sometimes-steep south and southeast facing slopes and hillsides.

Dalmatian toadflax is highly competitive in places where summer moisture is limited (xeric). It is often found in well drained, relatively coarse textured soils varying from coarse gravels to sandy loams.

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Habitat

Sites subject to invasion include areas of low interspecific competition, sparsely vegetated drier soils, and open rangelands. sites include roadsides, near dwellings, vacant lots, cemeteries, gravel pits, fields, waste areas, overgrazed pastures, and other disturbed sites.

Once established, the root system of Dalmatian toadflax makes it very competitive with other species, with infestations forming large colonies, displacing desirable vegetation. Because of this fact, it can significantly reduce crop yields, desirable livestock forage, and will stress native plant communities.

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ManagementEconomic Impact

Dalmatian toadflax is a California Class-A noxious weed. Noxious weeds are those plants that are considered by the state to be “troublesome, aggressive, intrusive, detrimental, or destructive to agriculture, silviculture, or sensitive nativespecies, and are difficult to control or eradicate".

Class-A rated noxious weeds are considered the most detrimental and are subject to mandatory enforcing actions including eradication, quarantine, containment, rejection, or other holding actions.

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ManagementEconomic Impact

In one 1992-study costs associated with managing Dalmatian Toadflax on one Montana Ranch averaged $40 per acre. Thirty percent of the 1,064 acres located on this ranch was severely infested with Dalmatian toadflax. As Dalmatian toadflax has been known to cause poisoning in cattle, the lost cattle-carrying capacity and lost land values associated with infestations increases the economic impact.

Studies on related toadflax have shown that infestation free plots produced 2.5 times more grass than plots where toadflax infestations were present.

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ManagementCultural Controls

Prevention. Disturbance appears to be closely related to the invasion potential of Dalmatian toadflax. Further, since seedlings of Dalmatian toadflax do not compete well for soil moisture against perennial and annual winter crops, it would be worthwhile to plant these types of crops to reduce the site availability.

Pulling. Dalmatian toadflax by hand may be effective for controlling small infestations, but pulling must be repeated several times a year for many years. Hand pulling, however, may not be practical with larger colonies as Dalmatian toadflax has an extensive underground network of lateral roots with numerous dormant root buds.

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ManagementCultural Controls

Mowing. Mowing has been shown to prevent seed production, but it will not remove it extensive lateral root system, which can extend down into the soil up to 10 feet. Mowing can also reduce the competitive effects of surrounding vegetation. Mowing can have the effect of dispersing toadflax seeds.

Cultivation. It was found that zero tillage practices could lead to infestations of Dalmatian toadflax. Therefore, intensive clean cultivation has been used to eradicate Dalmatian toadflax infestations. Cultivation needs to be done every 7-10 days during the growing season for at least two years. Cultivation is expensive and has ecological effects (soil structure destruction & increased erosion potentials). Cultivation can also bury Dalmatian toadflax seeds, which can remain viable for over ten years.

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ManagementBiological Controls

Literature search indicates that there are three insect species have the potential for being biological control agents for Dalmatian toadflax. However, studies that have been conducted so far have not yet proven that these insects may be effective in controlling Dalmatian toadflax:

a. Brachypterolus pulicarius is a shoot and flower-feeding beetle that feeds on young toadflax stems and shoot tips.

b. Calophasia lunula is a defoliating moth that is native of Eurasia and was introduced into the United States in 1968 to help control Dalmatian toadflax.

c. Gymnaetron antirrhini is a seed-eating weevil native to Eurasia that has been adapted to Dalmatian toadflax. Adults feed on young toadflax stems and larvae feed on immature seeds.

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ManagementChemical Controls

Herbicides Glyphosate, Dicamba and Picloram have been found to be effective in controlling Dalmatian toadflax. Their persistence and toxicity potentials make their application problematic.

a. Glyphosate. Alias: Roundup, Rodeo, and Accord. Glyphosate is recommended for spot treatments. Subsequent regrowth from deep and extensive root systems will occur the following year.

b. Dicamba. Alias: Banvel, Clarity, Vanquish, and Veteran. Dicamba is considered effective at controlling Dalmatian toadflax. Dicamba does not bind to soil and because of that may leach into groundwater.

c. Picloram. Alias: Tordon. Causes bending and twisting of the leaves and stems almost immediately.

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ManagementGrazing and Burning

Grazing. Overgrazing by livestock can increase Dalmatian toadflax’s competitive advantage, by creating a disturbed site. Timing of grazing can help reduce seedlings, but will not eradicate existing colonies. Dalmatian toadflax can be toxic to cattle. Sheep have been found to be effective at managing Dalmatian toadflax, as they are able to graze Dalmatian toadflax without toxic effect.

Burning. Burning is not effective as soil temperatures are not high enough to kill the extensive root system of the plant or any buried seeds. Burning can also destroy indigenous plants, increasing the competitiveness of toadflax. However, spot use of propane burners to destroy vegetative shoots has been shown to help prevent seed production.

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ManagementIntegrated Management

Prevention is the most practical and important means for the effective control of Dalmatian toadflax. Using desirable ground covers of perennials and annual crops will exclude Dalmatian toadflax. Further, Dalmatian toadflax will readily invade disturbed areas where open biological niche occurs. Filling these niches is essential in efforts to control Dalmatian toadflax.

Early detection is also an important effective control for Dalmatian toadflax. Community education is an important tool of an early detection program. When the infestations is small, there are far more options for the successful eradication. However, if an infestation is not detected until it occupies several acres, successful control is unlikely without great expense and the heavy and repeated use ofherbicides and other control methods.