Four views of Dalmation toadflax. From left: Entire plant; flower head; stem boring weevils; feeding damage from boring weevils. (Gary Stone Photos)
Dalmation Toadflax – invasive species in western Nebraska
By Gary Stone, Extension Educators, Panhandle Extension District
Early Detection and Rapid Response (EDRR) is a concept to identify potential invasive species prior to or just as the establishment of the invasive is taking place. An Integrated Pest Management plan (IPM) can be developed to manage, contain and eradicate the invasive species before it can spread further. This will avoid costly, long-term control efforts.
A potential invasive species that has been found in western Nebraska is Dalmatian toadflax. This perennial herb has been identified in parts of Nebraska, mostly in the Panhandle counties bordering Colorado, South Dakota and Wyoming. Dalmatian toadflax is either a state or a local noxious weed in Colorado, South Dakota, Wyoming and other western states.
Dalmatian toadflax is also known as broadleaf toadflax, wild snapdragon, and flaxweed. Its scientific name is Linaria genistifolia ssp. dalmatica (L.), of the family Scrophulariacea (Figwort family)
Originally from Eurasia and the Mediterranean, Dalmation toadflax was first reported in North America in the mid-1800s. It was brought to the United States as an ornamental, used as a yellow dye and for folk remedies. Dalmatian toadflax is distributed across most of Canada and the United States except the southeast.
Dalmatian toadflax is an herbaceous, short-lived perennial herb. It reproduces and spreads by seed and underground rootstocks.
Dalmation toadflax is a prolific seed producer. Large mature plants can produce up to 500,000 seeds per year. Seeds do not require a dormancy period before germinating and can remain viable in the soil up to ten years. Some seeds can germinate in the fall, but most germinate in April or May of the following spring.
Seed is spread by wildlife, vehicles, construction equipment, livestock, forages, feed grains, soil and gravel.
Dalmatian toadflax has an extensive root system. Lateral roots spread out 10 feet from the base of the plant and can extend downward 4 to 10 feet.
Dalmatian toadflax can grow to 2 to 3 feet in height. The leaves are generally broad, spade-shaped with smooth margins. The bases of the leaves wrap around the shoot. The leaves are waxy, which reduces the ability of herbicides to move into the plant.
Dalmation toadflax flowers are in the axils of the leaves in a spike at the end of each stalk. Flowers are yellow to orange in color and produces a two-cell fruit capsule, which contain the seeds.
Dalmatian toadflax is adaptive to a wide range of environmental conditions. This plant favors disturbed sites and is found in rangeland, pastures, waste areas and roadsides. Dalmatian toadflax is very aggressive and competes with native vegetation for soil nutrients and water. This plant will dominate the affected site in time, leading to an eventual monoculture.
Dalmatian toadflax has no forage value for livestock. It contains a poisonous glucoside that is harmful to livestock. Dalmatian toadflax is not harmful to sheep or goats.
Prevention is the best and cheapest management option. Detect infestations early and keep from spreading. Having well-established grasses and forbs on a maintained pasture or rangeland with proper grazing and rotational grazing techniques can go a long way to prevent its establishment.
Scouting, monitoring and proper identification are key factors for management. Infestations and spread of this weed can occur very rapidly.
Pulling or cultivating small Dalmatian toadflax plants can be an effective control method, as long as the plants are young, before they go to seed. The entire lateral roots need to be removed and an herbicide treatment may be necessary. Mowing alone will not control Dalmatian toadflax. Timely mowing can reduce the amount of seed produced.
Grazing Dalmatian toadflax seedlings with sheep can help prevent establishment. Grazing mature plants will not kill the plants and may stimulate new growth from the roots.
There are several insects that can have an effect on Dalmatian toadflax. The beetle, Brachypterolus pulicarius feeds on the ovary. Mecinus janthiniformus is a stem boring weevil that suppresses flower and seed production. Two other weevils feed on the seed capsule, Gymnaetron antirrhini and Gymnaetron netum. There is also a moth that defoliates up to 20 percent of the leaves on a single plant, Calophasia lunula. These biological controls may reduce the infestation of Dalmatian toadflax, but they will not control it. Other methods must be utilized in combination to reduce and control the infestation.
There are a few chemical treatment options available to manage Dalmatian toadflax. Products containing chlorsulfuron, dicamba, imazapic and picloram are shown to work.
Consult the specific herbicide label for instructions on how to treat Dalmatian toadflax for timing of application and rates. The waxy leaves and stems affect the coverage and uptake of the herbicides and cause erratic control. It is important to follow the product label unique to each individual herbicide.
When the herbicide label allows, the use of a crop oil concentrate (COC), methylated seed oil (MSO), or other oil-based adjuvants may improve herbicide penetration through the waxy leaf cuticle.
Retreatment of infested areas with Dalmatian toadflax may be needed due to the long life of the seeds.
Be sure to select a product labeled for the site. Read, understand and follow all label instructions when using any pesticide. Create an Integrated Pest Management plan (IPM) combining different control strategies to manage Dalmatian toadflax and promote the desired plant community you want.
This article is based on information from these sources:
Beck, K.G., “Biology and Management of the Toadflaxes”, Colorado State University, Fact Sheet Number 3.114
Goodwin, K. and Burch, D., “Watch Out for Toadflax”, Montana State University Extension, EB0181
Kadrmas, T. and Johnson, W.S., “Managing Yellow and Dalmatian Toadflax”, University of Nevada, Fact Sheet FS-02-96
Ogden, J.A. & Renz, M.J., “Dalmatian Toadflax (Linaria genistifolia ssp. Dalmatica)”, New Mexico State University Weed-Factsheet
USDA / NRCS Plant Profile, “Dalmatian Toadflax, Linaria dalmatica L."