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An Assessment of Exotic Plant Species of Rocky Mountain National Park

Linaria dalmatica ssp.dalmatica (L.) P. Mill (Linaria genistifolia ssp. dalmatica L.)
Dalmatian toadflax (Scrophulariaceae)


Current level of impact
Known locations in RMNP: Utility area, Horseshoe Park alluvial fan, Beaver Point.
Assessment: An intermediate number of patchy distributed populations. When added together, all populations would cover an estimated area of 5-10 hectares. Found in high quality areas with no known disturbance for last 100 years. Potential to invade and modify existing native communities.

Distribution
Origin: Southeastern Europe, native to Mediterranean region likely introduced as an ornamental.
Geographic distribution: Found throughout North America, although most common in western U.S. Various parts of Colorado from 5000 to 6500'.
Ecological distribution: Oak, aspen, sagebrush, mountain brush, and riparian communities. Roadsides, rangeland, waste places, cultivated fields, semi-arid regions. Tolerance for low temperatures and coarse textured soils.

Reproduction
Perennial, reproduces by seeds and underground rootstocks.
Seed dispersal: Seed dispersal is primarily by wind, but seeds can also be dispersed by livestock.
Seed longevity: Estimated seed longevity in soil is 10 years. Over 90 % germination has been obtained with 2-3 year old seeds in the laboratory.
Germination: Most seeds germinate the following spring, some germinate in fall after harvest.

Competition
Seedlings of toadflax are considered ineffective competitors for soil moisture with established perennials and winter annuals. Average stand life of toadflax once established is 3 to 13 years. Aggressive, can crowd out desirable forage on rangeland.
Level of impact: Noxious in many states. Spreads rapidly by rhizomes, and should be controlled quickly if encountered .

Control
Extensive, deep root system along with a waxy leaf make plant very difficult to control. Control methods for Dalmatian toadflax and butter and eggs are very similar.
Mechanical: Control can be obtained using clean cultivation, but requires 8-10 cultivations for the first year and 4-5 cultivations in the second year. Planting competitive perennial and winter annual grasses is also required.
Biological control: Currently, no biological control agents are considered widely effective.
Chemical: Herbicides registered for control of Dalmatian toadflax and butter and eggs include dicamba, 2,4-D, and picloram. Picloram at 2.25 kg/ha controlled Dalmatian toadflax for two years. Combinations of picloram at lower rates with fluroxypyr also are effective. Studies have found that the best time for application are when the carbohydrate reserves are lowest. For Dalmatian toadflax, the reserves are generally highest in the fall at the end of the growing season, and are lowest at the beginning of flowering (in the summer).
Other: Some reports indicate toadflax is poisonous and may be harmful to livestock. However, both Dalmatian toadflax and butter and eggs are considered unpalatable so reports of livestock poisoning are uncommon.

References

Morishita, D.W. 1991. Dalmatian toadflax, yellow toadflax, black hembane, and 
    tansy mustard: Importance, distribution and control. In James, L.F., J.O. 
    Evans, M.H. Ralphs and R.D. Child (eds.) Noxious Range Weeds. Westview Press. 
    Boulder, Colorado. 466 pp.

Saner, M.A. D.R. Clements, M.R. Hall, D.J. Doohan, and C.W. Crompton. 1995. The 
    biology of Canadian weeds. 105. Linaria vulgaris Mill. Canadian Journal of 
    Plant Science. 75:525-537.

Baig, M.N., K.N. Harker and A.L. Darwent. 1994. Tillage enhances yellow toadflax 
    (Linaria vulgaris Mill.) control with glyphosate. Weed Science Society of 
    America 34: 16 (Abstract #47).

Carder, A. C. 1963. Control of yellow toadflax (Linaria vulgaris) by grass 
    competition plus 2,4-D. Weeds 11:13-14.

Harris, P. 1961. Control of toadflax by Brachypterolus pulicatius (L.) (Coleoptera: 
    Nitidulidae) and Gymaetron anturhini (Payk.) (Coleoptera L. Curculionidae) 
    in Canada. Canadian Entomology 93:977981.

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