The issue: Yellow Toadflax

Yellow toadflax (Linaria vulgaris) is a creeping, spreading perennial that was originally brought to the US as an ornamental. It can grow up to three feet tall (usually shorter) and historically was also used to create yellow dye. It invades disturbed areas, roadsides, abandoned lots, overgrazed pastures and rangeland, after range fires, gravel pits and cultivated fields.

The yellow flowers, which resemble snapdragons, are borne in clusters at the ends of the stems and have a distinct, orange throat. The gray-green leaves are sessile, narrow, and taper at each end.

Yellow toadflax has an extensive rhizome (underground stem) system the leads to dense patches that choke out native plants. Seeds may be included in wildflower packets.

Yellow toadflax reproduces by seed and rhizomes. Kill the root and eliminate seed production. Seeds can remain dormant up to ten years in field conditions. The seeds are dispersed through water, wind, feather, fur, boats, muddy boots, vehicle tires, and clothing.

Integrated pest management options:

· Prevention: Don’t plant wildflower mixes that don’t identify the contents; keep ditch banks free of seed-producing weeds; identify and control new weed infestations; clean farming, recreational, and construction equipment and machinery between fields.

· Mechanical: Hand-pull small patches, removing as much root as possible. Tillage only encourages regrowth of the rhizome fragments.

· Cultural: Don’t overgraze pastures; manage land to provide good competition from desirable plants.

· Biological: Stem-mining weevil (Mecinus janthiniformis) is very effective.

· Chemical: Young plant and early bud stage — chlorsulfuron, dicamba, picloram (restricted use); fall, after first hard frost—imazapic. Be sure the weed and landscape or crop situation are listed on the label. Always read and follow herbicide label directions.

Combine them:

Combine different IPM options over a period of years to help improve the effectiveness of your efforts.

For more information, contact Ron Patterson, University of Idaho Extension horticulture/agriculture educator in Bonneville County, at 208-529-1390 or rpatterson@uidaho.edu.