Dalmatian Toadflax Biocontrol

What is Dalmatian Toadflax?

Dalmatian toadflax, Linaria dalmatica is an invasive perennial herb found in semi-arid areas on coarse-textured, gravely soils. It is usually associated with sparsely vegetated areas such as roadsides, abandoned or unmanaged land, gravel pits, and disturbed pastures and rangeland. It was brought to North America in the early 1900s for ornamental and medicinal purposes and escaped cultivation.

How to Identify Dalmatian Toadflax?

Dalmatian toadflax plants have a bluish, waxy appearance and can grow from 2 to 3 feet, sometimes taller. Leaves are heart-shaped and clasp the stem. Mature plants produce up to 25 vertical stems with bright yellow snapdragon-like flowers.

Effects of Dalmatian Toadflax?

Dalmatian toadflax can form a monoculture that severely reduces forage, productivity, biodiversity, and wildlife habitat. A mature plant can produce up to 500,000 seeds which are generally released through fall and winter. Some seeds may remain dormant in the soil for up to 10 years.

Biological Control

The insectary is currently working with the stem boring weevil, Mecinus janthiniformis to control Dalmatian toadflax. We do not recommend the closely related Mecinus janthinus for controlling Dalmatian toadflax. M. janthinus is used for yellow toadflax only.

Adult weevils overwinter in toadflax stems and emerge in the spring. After mating, female weevils lay their eggs in the stems of newly emerged toadflax plants. The larvae hatch from the eggs and begin to feed on the inside of the stem. When finished feeding the larvae will pupate within the stem and eventually become an adult. The adult feeds inside the stem until temperatures grow too cold for feeding. The adult then hibernates within the stem until spring when it chews its way out to continue the life cycle. One generation is produced per year.


What else does M. janthiniformis attack?

While Mecinus janthiniformis may feed on yellow toadflax, it cannot complete its development on yellow. It will not feed on any other plant in Colorado.

Will it kill the plant?

No, not initially, but the vigor of the plant can be greatly reduced. After many years, sites have been known to “collapse”, meaning that the large population of weevils will destroy the population of toadflax.

When is the best time to release the agents?

Anytime during the summer months when adults are available. Once the biocontrol agent is received, gently place the insects on the dalmatian toadflax.

How long will it take to control the weed?

It may take several years

Where do I get these agents?

You can place an order on the Request-A-Bug page.

What is the best release site?

In a thick infestation of toadflax that will not be sprayed with herbicide

Is there a charge?

Yes, the weevils are $30.00 per release of 200.

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