Toadflax | invasive-species

Yellow Toadflax - Dalmatian Toadflax

Linaria Vulgaris - Linaria Dalmatica

We are covering these two plants together because they are so similar in composition, biology and management.

What is it?

Yellow toadflax (Linaria vulgaris) and Dalmatian toadflax (Linaria dalmatica and Linaria genistifolia) are noxious, invasive perennial weeds that are found in Colorado at elevations from 5,000 feet to 10,000 feet. Toadflax thrives in disturbed and degraded areas such as overgrazed rangeland, abandoned lots, gravel pits, clearings, roadsides and fields (Colorado State University). Both species are expanding their infestations with Yellow toadflax taking over 40,800 acres and Dalmatian toadflax at 34,200 acres.

Why is it a problem?

The seeds of the Dalmatian toadflax germinate and emerge before the Yellow toadflax, which germinates and emerges in early to mid May. Dalmatian and Yellow toadflax shoots may grow from roots and can emerge in mid-March along the Front Range in Colorado however later emergence in June begins at higher elevations of 9,000-10,000 feet (such as on the Western Slope). The shoots of Yellow toadflax are 1-3 feet tall with narrow, linear 1-2 inch leaves that are pointed at both ends. Dalmatian toadflax shoots are between 2 and 3 feet tall with broad, waxy, spade leaves that wrap around the shoot.

Both toadflaxes readily spread from disturbed areas to undisturbed areas through the root system which can grow up 4 feet deep and 10 feet away from the parent plant for the Dalmatian toadflax. The Yellow toadflax foots can grow 3 feet deep and several yards laterally.

The flowers of the Dalmatian toadflax begin in late May and mid to late May for the Yellow toadflax. Flowering may not occur under drought conditions for the Yellow toadflax however.

Management techniques:

Since it is difficult to control both Toadflax species, management plans should be diverse and combine various control methods in order to ensure the development of the desired plant community while suppressing the toadflax. Control methods include:

Chemical herbicide application
Mechanical control such as mowing
Biological control using a defoliating moth (Calophasia lunula) or two-seed capsule-feeding weevils (Gymnaetron antirrhini and G. netum)

What can we do?

If this plant is found on your land in smaller populations, it is pertinent to manage this species in order to prevent spread and seed dispersal. These management techniques include:

Reduce or limit toadflax infestations by maintaining healthy plant communities on your property through grazing management methods to limit overgrazing.
Inspect hay and straw toadflax seed and purchase only certified weed-free hay and pellets to feed to horses located in areas within the back-country.
Identify, report, and eliminate new populations of toadflax as soon as possible.
Map identified infestations and keep records every year of these infestations.
Utilize a combination of mechanical, biological, cultural, and chemical methods for most effective control of toadflax.
Ensure monitoring takes place and implement a follow-up treatment plan for plants and seedlings that have been missed.

This invasive species is difficult to control in large populations and a management plan should be created if this plant is located on your property. Using multiple applications of herbicide at specific times in the season will increase your chances of suppression or removal altogether.

Entities working on this invasive in the Gunnison Basin:

Yellow Toadflax is included in the BLM and Noxious Weed Plan. A hard copy can be reviewed at the BLM Gunnison Field Office located at 210 West Spencer Street, Gunnison, CO 81230.

The USFS is doing research in collaboration with other agencies in the Gunnison Basin to perform monitoring, management and research on these invasive species in regards to Yellow Toadflax. If you contact the USFS at 970-641-0471, they can provide you with information.

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