What is Yellow toadflax?
Yellow toadflax, Linaria vulgaris, is a common herbaceous weed across much of North America. It prefers well-drained coarse soils in disturbed, open habitats and can grow at high elevations. This native of southeastern Europe and southwestern Asia was intentionally introduced to North America as early as the mid 1700s for horticultural and medicinal purposes.
How to Identify Yellow Toadflax
A mature yellow toadflax plant can produce several woody upright stems. Stems are usually reddish at the base, becoming more tender and succulent toward the growing tip. Leaves are 1 to 2 inches long, linear, and pointed with a narrowing, tapered base. Snapdragon-like flowers are pale yellow with a bright orange bearded throat. A mature plant can produce from 15,000 to 20,000 seeds per plant.
Effects of Yellow Toadflax
Yellow toadflax produces a deep-rooted taproot along with creeping horizontal roots. This helps the plant compete for water and nutrients and allows for a monoculture presence among other plants. The spreading roots can produce up to 100 shoots during the first summer. New infestations are probably started by seed.
The insectary is currently working with the stem boring weevil, Mecinus janthinus to control yellow toadflax. We do not recommend the closely related Mecinus janthiniformis for controlling yellow toadflax. M. janthiniformisis used for Dalmatian 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 does Mecinus janthinus attack?
While Mecinus janthinus may feed on Dalmatian toadflax, it cannot complete its development on Dalmatian. It will not feed on any other plant in Colorado.
- Will it kill the plant?
Not initially, but the vigor of the plant can be greatly reduced.
- How long will it take to control the weed?
It may take several years.
- 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 100.