Scout winter wheat at green-up to make informed, early-season weed control decisions

Popular herbicide options have a short window for effective application in winter wheat.

As the snow melts, winter wheat producers in Michigan should prepare to scout their crop for weeds. Weed pressure reduces wheat yields through competition with the crop for nutrients, moisture and light. Weeds that grow unchecked can also compromise crop quality and complicate harvest. Scouting fields in April while wheat is producing tillers allows growers to assess weed pressure and promotes timely control decisions.

Scouting procedures should be designed to collect a representative sample of the weed community in each field. Walking a wide zigzag pattern is frequently recommended to efficiently cover the breadth of a stand. Field size can be used to determine the appropriate number of observations to take while moving through a scouting pattern. Fields of less than 40 acres warrant a minimum of five stops. Larger fields can be accurately evaluated by surveying one site for every eight acres in area. At each site, a scout should observe 100 square feet of ground to identify and record what weed species are present, as well as their density and stage of growth.

Winter annual weeds like common chickweed, henbit, horseweed (marestail) and purple deadnettle are often found in winter wheat because their lifecycles align with the crop. Like wheat, winter annuals germinate in the late summer or fall, go dormant over the winter, and emerge in spring to flower and set seed. Winter annual weeds are most successfully controlled when actively growing, but before bolting in spring. Early emerging summer annuals, biennials and perennial weeds can also present a challenge in winter wheat, especially in thin stands with late canopy development.

Common chickweed
Common chickweed (Stellaria media) is a winter annual weed
that frequently infests winter wheat in Michigan. Photo credit: Robert Vidéki, Doronicum Kft.

Many factors such a weed species, density and crop health influence weed-crop competition. However, percent ground cover by species can be used as a general measure of weed pressure, with less than 5 percent cover indicating light pressure, 5 to 30 percent moderate, and more than 30 percent a severe infestation. In a well-managed crop, light pressure from a less competitive species, such as henbit, may not require control. In the case of moderate to severe infestations, producers should consider applying an herbicide, taking into account the economics of control including anticipated crop yield with and without control, market price and the cost of herbicide application.

Herbicide selection should be based upon what weed species are present in the field and the crop’s stage of growth. Many popular herbicide options have a limited window for application in winter wheat. Late herbicide applications are less effective in controlling weeds and generally have a greater potential to injure the crop, ultimately reducing yield.

For more information on weed control in winter wheat, including specific herbicide recommendations, visit the MSU Weed Science website or access the Michigan State University Extension 2013 Weed Control Guide for Field Crops.

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