Yellow toadflax

Yellow toadflax is an herbaceous perennial in the Plantaginaceae (plantain), formerly Scrophulariaceae, family. It produces erect stems usually between 1 to 2 feet tall and occasionally reaching 3 feet tall. Stems are slightly woody at the base and waxy and herbaceous toward the tops. Leaves and upper stems are blue green to green in color. Leaves are thin and linear, and they have smooth margins and are waxy. Leaves occur alternately and clasp the stem. Vegetation gives off an unpleasant, musky odor when crushed. Yellow toadflax flowers from early summer to fall. Flowers resemble snapdragon flowers and occur on dense racemes at the end of stems. Each flower is yellow, approximately 1 inch long, and has two “lips”, an upper and lower. Flowers have an orange bearded throat that is usually apparent from a distance, giving yellow toadflax its alternate common name “butter and eggs”. Flowers also have a long spur on the bottom. Yellow toadflax has an extensive root system made up of lateral rhizomes. Seeds are produced in capsules and are small, flat, dark brown with thin wings.

Yellow toadflax produces quinazoline alkaloids and may be poisonous to livestock; however, it is generally avoided by cattle and horses. Goats and sheep have grazed yellow toadflax without apparent effect.

Yellow toadflax is native to Eurasia and the Mediterranean, and it was introduced to North America in the mid-17th century as an ornamental. It creates dense patches and infestations by spreading rhizomes and seeds and spreads to new locations by seeds and root fragments. This species is frequently found in rangeland, sagebrush steppe, disturbed sites, and hay fields.

Prevention and cultural control strategies should be utilized as much as possible.

There is only one biological control agent available for yellow toadflax in Teton County. The stem mining weevil (Mecinus janthinus) has been released throughout Teton County; however, infestations are frequently too far away from each other for the agent to spread on its own. Please contact TCWP for assistance in collecting and/or releasing this agent.

Hand pulling and digging out of the taproot and all lateral roots can be effective if conducted prior to establishment in an area, but great care must be taken to ensure that all of the root system is removed. Tillage may be effective, but must be repeated every 7 to 10 days and for multiple years. Mowing is not recommended for control as it stimulates root and rhizome growth. Controlled grazing is not effective as livestock do not preferentially graze yellow toadflax thereby reducing competition from desirable species .

Large infestations can be controlled with herbicides. Spring treatments prevent flowering and seed production, and fall treatments may be effective at killing the root system. Read the label before using any herbicide. Contact TCWP if you have any questions about application rates or how to use an herbicide.

• Weed Report: Yellow toadflax (2013) DiTomaso, J.M., G.B. Kyser et al. Weed Control in Natural Areas in the Western United States. Weed Research and Information Center. University of California.
• Yellow Toadflax. Washington State Noxious Weed Control Board.
• Yellow Toadflax, Linaria vulgaris. Mahr, S. University of Wisconsin-Madison. Wisconsin Horticulture.
• Biology and Management of the Toadflaxes (2014) Beck, K.G. Colorado State University Extension. Fact Sheet 3.114
• Field Guide for Managing Dalmatian and Yellow Toadflaxes in the Southwest (2014) United States Department of Agriculture Forest Service