University of Maryland Extension

Weed of the Week - Blue Mustard

Author: 
Chuck Schuster
Blue Mustard

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Blue Mustard, Chorispora tenella, is becoming a concern in some nursery settings. Not native to this area, it may arrive with nursery liners. It is a fall germinating winter annual, and a prolific seed producer. A native of the Soviet/Asian continent, it entered this country in the late 1920’s most likely in small grain seed. Blue Mustard will germinate in the late fall; produce a rosette that will have deeply lobed leaves, similar to that of a dandelion. Leaves are alternate, oblong in shape with a small petiole on the lower stem leaves. Upper stem leaves will be sessile. Leaves that are produced on the flowering stem will be coarsely toothed with wavy margins. It has a shallow taproot, and will grow to about eighteen inches in total height. It will grow in a wide range of moisture and soil fertility conditions. The flowers will have four petals and will be blue to purple in color. Viable seed will be produced within ten days of the flowers opening.

Control of this weed is important. It is considered invasive in certain states, but not in Maryland. The best time for post emergent control of blue mustard is in late winter to early spring, when growth resumes. Control methods should be used before mid-April at the very latest. In open settings, a 2, 4D product will work very well. Cultivation prior to the production of flowers is also useful. Dicamba as a selective post emergent is also labeled and works well. Pre emergent control can include Surflan (oryzalin) and Snapshot (trifluralin and Isoxaben) products but they would need to be applied in late summer. Clopyralid (Lontrel) has been shown to have effect on this weed, and can be used over the top in nursery settings. Use caution, as it will create some plant damage. Casoron (dichlobenil) has been shown in some areas to be effective and can be used in the nursery setting. In the non-selective areas, gramoxone is a good contact defoliant, and glyphosate products will also work. When using glyphosate products, do not allow product to come into contact with exposed roots, suckers or trunks and stems.

 

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