Overview
Yellow toadflax (Linaria vulgaris), also called butter and eggs or wild snapdragon, is one of about 130 species of Linaria native to Eurasia. Many weedy species of Linaria resemble true flax (Linum usitatissimum) in leaf shape and arrangement. Yellow toadflax is an escaped ornamental brought to the US in the mid-1800s. It was used as a yellow dye for centuries in Germany, so immigrants, especially the Mennonites, cultivated it for use as a dye plant.
This short lived perennial plant in the figwort family (Scrophulariaceae) occurs throughout most of temperate North America and is listed as a noxious weed in several western U.S. states and Canadian provinces.
Because it contains a poisonous glucoside that are mildly toxic to livestock when consumed in large quantities, it is a particular problem in rangeland (although it is also unpalatable, so reports of livestock poisoning are rare). It is typically found in open, disturbed sites such as roadsides and waste areas or in fields, pastures, edges of forests and rangeland, where it can displace desirable grasses.
This species is occasionally used in flower gardens, but it is not a good ornamental for Wisconsin due to its aggressively spreading nature and ability to escape from cultivation. It has also been included in wildflower mixes, so check the species list of mixes carefully, and avoid mixes that don’t identify their contents.
The related Dalmatian toadflax (L. dalmatica, from southeastern Europe around the Mediterranean) is another escaped ornamental that is very similar to yellow toadflax. It is a larger, more robust plant with increased branching near the top of the plant and a different type of leaf. It was introduced in North America around 1900. Dalmatian toadflax is a prohibited invasive in most of Wisconsin, and restricted in Juneau and Bayfield counties.
The easiest way to distinguish between yellow and Dalmation toadflax is by the leaves. The lance-shaped, gray-green, 2 inch long leaves of yellow toadflax are stalkless and pointed at both ends. Dalmatian toadflax has clasping, heart-shaped or egg-shaped leaves. The leaves of both species are alternate but may appear to be opposite because they are crowded together.
The plants begin growing from the roots as soon as the soil warms in early spring. Plants can grow up to 3 feet tall, but are generally much shorter (1 to 2 feet tall).
Yellow toadflax spreads both by seed and extensive creeping rhizomes and forms patches. The roots of a single plant can extend 10 feet and give rise to daughter plants every few inches. This aggressive perennial is able to quickly colonize open habitats and often outcompetes other plants, including natives. Plants growing in dry soils tend to be stunted but are relatively persistent.
In the summer through fall, bright yellow or cream snapdragon-like flowers are produced in crowded terminal clusters (the flowers of Dalmatian toadflax occur in the axils of the upper leaves and bracts and bloom earlier in the season). Each of the 1 inch flowers has an orange spot on the lower lip (orange bearded throat) and a ½ inch long straight spur. As the flowers mature, the orange patch becomes more distinct. The flowers are attractive to bees, butterflies, and other insects.
Round, dark colored seeds are produced in brown, globe-shaped capsules. Each seed has a notched, papery collar that aids in dispersal. Although seed viability is generally low, the winged seeds may disperse over a long distance in the wind, or may be moved by water and ants. Seeds may remain dormant in the soil for up to 10 years.
Control of Yellow Toadflax
Yellow toadflax can be difficult to eradicate due to its extensive root system, which can spread as much as 10 feet. Root fragments as small as ½ inch long can produce new plants. Tillage beginning in the early summer and continued at 3 to 4 week intervals has been somewhat successful in controlling this weed. Mowing will help decrease seed production but will generally not eliminate established populations. Burning is not effective, as it does not kill the roots and can promote resprouting. Hand pulling can be effective, as long as roots are removed.
Many populations have developed resistance to herbicides. The best time for herbicide treatment is during or just after flowering. Note that products containing glyphosate or triclopyr are not effective for controlling yellow toadflax.
Several biological control agents (a defoliating moth, a seed head weevil, and a flower beetle) have been released in the west, and they provide from fair to good control. The weevil Gymnetron antirrhini, which develops inside the fruit as a larva and feeds on the leaves, buds and stems as an adult, is the most important species in many parts of North America. Other species include another weevil (Mecinus janthinus) that bores in the stems as larvae and feeds on shoots as adults; the leaf-feeding moth Calophasia lunula, which has a very limited distribution; and another moth species (Eteobalea serratella) that mines the roots. This last species reduces the competitive ability of yellow toadflax, shortens the flowering season and lowers seed weight, and complements other biocontrol agents.
Author: Susan Mahr, University of Wisconsin—Madison
Reviewers: Allen Pyle, Horticulture Outreach Specialist, UW—Madison Extension, Bruce Spangenberg, Horticulture Outreach Specialist, UW—Madison Extension
Revised: September 2026
