Flixweed (Descurainia Sophia) is a common weed that is in full bloom throughout much of the Front Range in May. This spring blooming annual was introduced unintentionally to North America, and is on the noxious weed list in 46 states. It owes its success to its early spring germination, adaptability to many soil types and waste areas, and its prolific seed production.

Flixweed is commonly found as weed in alfalfa, wheat, barley and oat fields, and frequents road sides, gardens and waste areas.

As a member of the mustard family, flixweed closely resembles another common weed called Tansy Mustard (Descurainia pinnata). Both have erect stems that branch, ranging to 30" in height depending on the growing conditions. The leaves are alternate, two to four inches long and finely dissected to give a lacy appearance. The stems and leaves are covered with fine hairs. Flowers are small, pale yellow, four-petalled and are produced in sequential small clusters at the tips of elongating stems and branches. (The picture shows flixweed with the typical terminal flowers, and thin seed pods) The seed pods are a half to one inch in length and stalked. The longer, slender seed pods of flixweed differentiate it from the shorter and thicker tansy mustard seed pods. In Colorado, flixweed is the more common of the two species.

Flixweed makes the noxious weed list because it is a rapidly invasive weed that crowds out other useful plants. It is economically important because it depletes the value of rangelands, and when growing in alfalfa fields, decreases the nutrient quality of the hay produced. Most animals will eat the plant in the early spring before it develops flowers, but thereafter it is much less palatable. Cattle grazing large amounts of flixweed in the spring can develop photosensitization that appears as severe sunburn of the white skinned areas.

Flixweed incorporated in poor quality hay may be eaten by livestock if they are hungry enough. Small quantities (a few mouthfuls) of flixweed are unlikely to harm any animal. Large amounts with seed pods may affect pregnant animals. Like many other mustards, flixweed contains substances called glucosinolates especially in the seeds, which interfere with iodine metabolism and can produce goiter (thyroid enlargement) in the new born fetus. It is therefore important to feed weed-free hay to pregnant animals.

Control of flixweed is relatively simple and can be accomplished by mowing or pulling the plants before they flower and form seeds. Eliminating the seed-bank will prevent the recurrence of this annual. Various herbicides (Trisulfuron, MCPA, bromyxnil) can also be used to control flixweed. The best product, application rate and timing for use of these herbicides in your area can best be determined by your local Cooperative Extension weed specialist or the local county weed district.

The authors have received training through Colorado State University Cooperative Extension's Master Gardener program and is a Master Gardener volunteer for Larimer County.

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This page updated:  May 31, 2007