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Linaria genistifolia (L. dalmatica), L. vulgaris--Dalmation and Yellow Toadflax
Figwort Family
About Dalmation and Yellow Toadflax: Toadflax is native to the Mediterranean region of Europe. The plant was introduced to the western U.S. as an ornamental about 1874. The leafy plants of some species look much like the unrelated flax plants, and the flowers somewhat resemble toads, hence the name "toadflax".
The toadflaxes first appeared in Montana in the 1940's, and they have become widespread since then. Like many other noxious weeds, toadflax thrives in dry, exposed soils on rangeland or along roads. Toadflax seedlings are poor competitors for soil moisture, but once established the plants develop a vigorous spreading root system. New plants develop from the root buds or from seeds. A single plant can produce a half million seeds. The plants live for about five years and the seeds remain viable in the soil for up to ten years.
Medicinal: Medicinally, Linaria vulgaris is reported to be astringent, bitter and acrid, useful to stimulate liver function, or as a wash for skin diseases. The plant reportedly produces a fly poison if boiled in milk. In Sweden this milk was placed where flies were problematic.
Mechanical Controls: Small patches of toadflax can be hand-pulled for five or six years to deplete the energy reserves of the root system. Viable seeds in the soil may continue to germinate for 10 to 15 years. Mowing reduces seed production, but does not deplete the root system. Repeated cultivation does, but it takes a lot of work. A patch should be cultivated early in the season, and repeated every 7 to 10 days the first year, with 4 or 5 additional passes the second year, and monitoring afterwards. Thats a lot of cultivating! Seeding the sites to maintain control is also required.
Biological Controls: Two insects are already widely distributed on toadflax infestations across the northern states and Canada. A small black beetle (Brachypterolus pulicarius) damages the tips of the shoots, preventing many of the flowers from developing. The insect can reduce seed production by up to 75%. A fruit-feeding weevil (Gymnaetron antirrhini) feeds in the flowers and reduces seed production by up to 80%. These insects may slow the spread of the toadflaxes, but may not reduce the size of existing infestations. Other insects that have been introduced to control the toadflaxes include two root-boring moths (Eteobalea intermediella and Eteobalea serratella) a root-galling weevil (Gymnetron linariae), another fruit-feeding weevil (Gymnetron netu), a stem-boring weevil (Mecinus janthinus), and a moth that feeds on the leaves and flowers (Calophasia lunula). There is a concern that this moth could attack native snapdragons of California, so redistribution of the insect is now discouraged.
Grazing: Livestock and wildlife do not favor toadflax, but they do browse on it some. There is little documentation available on the impacts of either grazing or trampling the plants. However, since the seedlings are poor competitors for soil moisture, trampling may stimulate other plants to out-compete them. Caution is advised if the plants are grazed while producing seed. The seeds could be passed through the manure and spread to new habitat. More studies need to be done with livestock on these weeds.
Chemical Controls: The toadflaxes are hardy plants with waxy leaves and extensive root systems. Even the most potent herbicides have mixed results. Herbicides that have been used with some success include dicamba (Banvel¨-pre-bloom), chlorsulfuron (Telar¨ DF-spring or fall) and picloram (Tordon¨ 22K-pre-bloom or fall.), but repeat applications are required to achieve full control. Spraying is reportedly most successsful at the beginning of flowering when carbohydrate energy reserves in the roots are lowest. Spot applications of glufonsinate-ammonium (Finale¨-spring) or glyphosate (Roundup¨-fall) may be more effective and less hazardous.
Important: Most "weed problems" are really "people problems" from poor land management and a lack of ecological insight. It is easy to reach for a tool like fire, mowing, or herbicides to attack an out-of-control weed, but often those tools do little to get to the root cause of the weed infestation, and sometimes make the problems worse. You must read the range ecology sections of this website before applying any tool of weed control. Return to the Wildflowers & Weeds Home Page for articles on Desertification and Noxious Weeds.
Notes
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