The issue: Dalmatian toadflaxes
Dalmatian toadflaxes (Linaria dalmatica and Linaria genistifolia) are perennials from the Mediterranean and Eurasia regions. L. dalmatica is more common in the western US, but L. genistifolia has been identified in Oregon and Washington.
Dalmatian toadflax was first introduced to the US as an ornamental in 1874. It infests disturbed areas, roadsides, gravel pits, pastures and overgrazed rangeland. It is toxic to cattle, but not sheep and goats.
Dalmatian toadflax can grow up to four feet tall. The bright yellow flowers resemble snapdragons and often have a red- or orange-tinged throat. The waxy, blue-green leaves are broad-based, taper to a point, sessile (no petiole), and clasp the stems.
Dalmatian toadflax reproduces by seed and rhizomes (underground stems). One plant may produce up to 500,000 seeds and seeds can remain viable up to ten years in field conditions. Seeds may spread through water and soil movement, snow runoff, and somewhat with wind.
Integrated pest management options:
· Prevention: Keep ditch banks free of seed-producing weeds; always be on the lookout for new weed infestations; feed weed-free hay; clean equipment and machinery between fields.
· Mechanical: Hand-pull or cultivate every 7 – 10 days for several years, remove as much root as possible. Pull seedlings within eight weeks after germination, before they reach the perennial stage.
· Cultural: Don’t overgraze pastures; manage land to provide good competition from desirable plants; revegetate disturbed areas.
· Biological: Sheep or goat grazing; stem-mining weevil (Mecinus janthiniformis).
· Chemical: Best effect in spring before blooming; dicamba, picloram (restricted use herbicide), imazapic, or chlorsulfuron. Be sure the weed and landscape or crop situation are listed on the label. Always read and follow herbicide label directions.
Combine different IPM options over a period of years to help improve the effectiveness of your efforts.