Virginia Tech Weed Identification Guide

Wild Mustard: Brassica kaber

Weed Description:  Most often a winter annual but sometimes a summer annual with characteristic yellow mustard flowers.  This weed can be found throughout the United States primarily in nurseries and winter small grains.
Seedling:  Cotyledons kidney- to heart shaped, approximately 5 mm long and 8 mm wide and have indentations at the apex.  First true leaves are alternate, hairy, elliptic in outline and have wavy margins.

Roots:  Taproot in combination with a fibrous root system. 

Leaves:  Alternate, egg-shaped to ovate in outline, approximately 2 to 8 inches long and 1 1/2 to 4 cm wide.  Lower leaves occur as a rosette, are petiolated, and unevenly lobed with toothed margins.  Upper leaves become progressively smaller up the stem, are not lobed, and either clasp the stem or have short petioles.
Stems:  Erect, branched towards the top of the plant and usually have hairs at least at the base of the plant but hairs can also be absent. 
Flowers:  Produced in clusters at the ends of branches.  Individual flowers consist of 4 yellow petals and are approximately 3/4 inch wide.

Fruit:  A silique that is approximately 1 to 2 inches long and 2 to 3 mm wide.  Siliques occur on flower stalks that are approximately 5 to 7 mm long and are rounded in cross-section but have a 4-angled flattened beak at the tip that is a little less than half as long as the pod.

Identifying Characteristics:  Generally a plant with a winter growth habit that has typical yellow mustard flowers and irregularly lobed leaves with wavy margins toward the base of the plant and much smaller, unlobed leaves at the top of the plant.  At maturity the flowers of several mustard species, including Yellow Rocket (Barbarea vulgaris) and Wild Radish (Raphanus raphanistrum), resemble those of wild mustard. However, wild radish has leaves that are covered with stiff hairs unlike either wild mustard or yellow rocket.  Additionally, the large terminal lobe in the leaves of yellow rocket helps to distinguish this weed from wild mustard.