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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 1900’s for ornamental and medicinal purposes and escaped cultivation.
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.
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.
There are a number of Dalmatian toadflax agents to help control the spread of this noxious weed. The insectary is currently working with the stem boring weevil, Mecinus janthiniformis, and the foliage feeding moth, Calophasia lunula. We do not recommend M. janthinus for controlling Dalmatian toadflax.
For the stem boring weevil, adult females lay their eggs in the stems of the toadflax in the spring. 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 emerge as an adult. The adult stays within the stem until spring when it chews its way out to continue the life cycle. One generation is produced per year.
For the foliage feeding moth, the adult female lays her eggs on the foliage of the toadflax and then the larvae begin to feed on the leaves of the plant. After 5 instars, or molts, the larva will pupate in the soil surrounding the plant and emerge as an adult. Two to three generations are possible in each year.
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