What is in this article?:
- Cold Arizona temperatures likely lowered aphid and thrips numbers in winter vegetables;
- As the winter lettuce season end nears, powdery mildew can be an economic concern in some lettuce fields;
- The weed shepardspurse has become increasingly widespread in recent years.
By Barry Tickes, UA Area Agriculture Agent
We continually select for those weed species that thrive under our production practices and escape current control techniques. Shepardspurse is one of several weed species around for a long time but that growers and pest control advisors have seen become increasingly widespread in recent years.
The botanical name for shepardspurse is Capsella bursa and it is in the mustard or crucifer family. This is a large family of plants and includes many common weeds including London rocket, sahara mustard, and black mustard. It also includes many of the crops grown here including broccoli, cauliflower, cabbage, bok choy, kale, arugula, kohlrabi, mustard greens, daikon, and others.
Almost all of the plants in this family are valued for nutritional or medicinal properties. Many of the weeds are used for medical purposes. Shepardspurse was frequently used during the World War I to control bleeding. It can be difficult to control shepardspurse selectively in many brassica crops because of its similarity.
It is the physical characteristics of the weed that is largely responsible for its spread. The foliage of shepardspurse is characteristically a low growing rosette that is often covered and can be difficult to reach with herbicides.
The seed head, on the other hand, grows 12 to 20 inches above the vegetative parts and has been reported to produce as many as 50,000 seeds per plant in a single season. The seeds are very small and can float in water and blow in the wind.
The seeds germinate at very shallow depths. Soil active herbicides can fail if they are not concentrated at the soil surface. Shepardspurse proliferated in alfalfa during the years when 2, 4-DB (Butoxone, Butyrac) was the primary broadleaf herbicide used because 2, 4-DB is ineffective on this weed.
In vegetable crops, shepardspurse can be controlled with Kerb on the crops it is registered and if it is concentrated at the surface. It is less effective if some of the herbicide leaches below the germinating seeds. Prefar, Dacthal, Balan and Prowl are mostly ineffective on this weed.
Contact Tickes: (928) 580-9902 or firstname.lastname@example.org.