Tansy Mustard, Western Tansy-mustard

Descurainia pinnata



Tansy Mustard is an annual cool-season forb growing to 2 feet or 0.6 m tall. It is usually single-stemmed, leafy, and covered with fine, gray hairs. Leaves are placed alternately along wavy stems, with each divided into many small segments. Leaves are broadly lance-oblong in outline with numerous deep to shallow lobed divisions.  Flowers vary from yellow to whitish, occurring in long clusters at stem ends. Plants flower in February through May. The fruit is a straight to slightly curved seed pod up to about half an inch or 1.2 cm long. Each seed pod has two rows of 10 to 20 seeds. 


Tansy Mustard is distributed widely throughout the southern and western United States up to 7000 feet in elevation. Heavy stands may form on dry, sandy soils in arid areas. Plants can occur in areas with soil disturbance such as roadsides or near railroads as well as in less disturbed habitats. Abundance increases after moderate or heavy winter rains in the arid southwest.  

Toxic Agent

The toxic agent is unknown. Large quantities of the plant must be consumed before poisoning occurs. Tansy Mustard also accumulates toxic levels of nitrate. Seeds contain toxic isoallyl thiocyanates and irritant oils. Large quantities must be consumed over a long period of time for poisoning to occur. 

Signs of Livestock Ingestion

Cattle are the only kind of livestock reported to be poisoned. The first clinical sign is partial or complete blindness (blind staggers). Animals wander aimlessly until exhausted, or may stand pushing their head against a solid object for hours.  Next, or along with the blindness, comes an inability to use the tongue or to swallow (paralyzed tongue). Cattle may stand at water unable to drink or try unsuccessfully to graze.  

Management Strategies

A simple and effective treatment is to administer 2 to 3 gallons of water (with nourishment such as cottonseed meals if the animals are seriously weak) twice daily by stomach tube. With this treatment, clinical signs gradually disappear.  Tansy Mustard is relatively non-toxic, so moderate amounts may be desirable. Furthermore, stands thick enough to lead to the heavy consumption necessary for poisoning do not appear every year. Because of this, herbicidal control is not recommended except where dense stands occur near watering, holding facilities, and other areas of high livestock use.  Good range management practices and grazing a mixture of cattle, sheep, and/or goats may help prevent excessive intake by cattle.