Yellow Toadflax Biocontrol

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 1700’s for horticultural and medicinal purposes.

How do I recognize 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. 

What are the 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.

Biocontrol of yellow toadflax:


As with Dalmatian toadflax there are a number of agents to help control the spread of this noxious weed.  The insectary is currently working with a stem boring weevil, Mecinus janthinus and a foliage feeding moth, Calophasia lunula. 

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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