Issue No. 20, Article 4/August 8, 2008
Controlling Weeds in Wheat Stubble Fields
Wheat stubble fields in which double-crop soybean are not planted often become populated with a robust crop of several summer annual weed species. Common examples include velvetleaf, common ragweed, pigweed and waterhemp, foxtails, and fall panicum. Even though many of these plants emerged relatively late in the growing season, they can produce large amounts of seed if allowed to reach maturity.
Farmers have several options to control weeds in wheat stubble fields, including mowing, tillage, and herbicides. For the highest level of success, these options should be implemented before any weeds begin to produce seed.
Mowing can effectively reduce the amount of weed seed produced by established broadleaf species. The shredder or sicklebar mower should be adjusted to cut as close to the soil surface as possible. Mowing may not completely eliminate weed seed production, since some seed could be produced from plants that regrow or from tillers present on grasses below the height of cutting. It can help reduce seed production of simple perennials (such as common pokeweed), but it does less to contain the expansion of perennial species that can spread by underground rootstocks (such as Canada thistle and johnsongrass).
Tillage is another viable option to control weeds in wheat stubble. Large weeds may be more effectively controlled with an "aggressive" implement (such as a tandem disk) than a less-aggressive one (such as a field cultivator). While effective at controlling established weeds, keep in mind that tillage can stimulate germination and emergence of additional weeds. Fuel consumption and cost and the potential for soil erosion are additional factors to consider when using tillage to control weeds in wheat stubble fields.
Herbicides and herbicide combinations are available that can provide very broad-spectrum control of weeds in wheat stubble fields. Glyphosate, 2,4-D, and dicamba are examples of herbicides that can be applied alone or in combination. Be sure to refer to product labels for application information, such as rates, additives, and rotational intervals. As always, take precautions to reduce drift of spray particles or vapor from the target area.--Aaron Hager