2 Scouting for Common Weed Problems

    One of the best ways to combat weed infestations in alfalfa is to establish a thick, vigorous, healthy stand that will successfully compete with invading weeds. Although weeds generally require the same conditions as alfalfa, they are often able to grow more vigorously than the crop with less moisture and lower nutrient levels.
    In general, weeds appear in thin or poorly growing stands of alfalfa. Therefore, one of the best weed management practices is to make as many factors as possible favorable for the alfalfa plant. Winter annual weeds invade dormant alfalfa and can reduce first-cut yields. Effective control of chickweed for three years has increased first-cut alfalfa hay yields by I ton. The presence of grassy weeds can reduce the life of the alfalfa stand.
 

Winter Annuals

Seedling Alfalfa
    Scout fields regularly following alfalfa emergence for problem weeds: chickweed, ryegrass, annual bluegrass, and volunteer small grains. Apply the appropriate herbicide after alfalfa has reached the first trifoliate leaf stage or beyond.

Established Alfalfa
    The best time to start scouting for winter weeds is in October and November; however, scouting in February and March will help you plan treatments for the following fall. Problem weeds in established alfalfa are chickweed, cornflower, henbit, mustards, shepherds-purse, pepperweed, ryegrass, and knawel. Although scouting takes place in spring and fall, treat in the fall - preferably between November 15 and December 30. Use appropriate chemical control if weeds comprise more than 20 percent of the plants in the field.
 

Summer Annuals

Established Alfalfa
    Problem weeds in established alfalfa are crabgrass, goosegrass, fall panicum, foxtails, ragweed, pigweeds, and lambsquarters. Many summer weeds, especially grassy weeds, begin to appear after the first and second cutting. Broadleaf weeds tend to be more severe during the first year of establishment. Apply a preeinergence herbicide if annual grassy weeds have not germinated and are known from previous scouting to be a potential problem. If grassy weeds have emerged and have a good leaf area, apply the proper herbicide for postemergence control. Treat broadleaf weeds if they comprise more than 20 percent of plants in the field.
 

Perennials in Established Alfalfa

    Problem grasses are johnsongrass, bermudagrass, and fescue. Problem broadleaf weeds are curly dock and plantains. Apply the proper postemergence herbicide for johnsongrass and fescue control, which will also suppress bermudagrass. Seedling curly dock can be controlled with the appropriate herbicide. Larger plants can be only partially suppressed. Treat when weeds comprise mote than 20 percent of plants in the field.