No. 20 Article 7/August 5, 2005

Weed Control in Wheat Stubble Fields

Wheat harvest marks the end of one cropping cycle and the beginning of a second. In parts of central and southern Illinois, farmers frequently opt to plant double-cropped soybean following wheat harvest, with hopes that the first "killing" frost will be late enough to allow the soybean to reach maturity. Wheat stubble fields in which no second crop is planted often become populated with a "crop" of summer annual (and sometimes perennial) weed species. Unlike double-cropped soybean, farmers should not allow these plants to reach maturity and produce seed.

Often, several different summer annual weed species populate wheat stubble fields. Common examples include velvetleaf, common ragweed, pigweed and waterhemp, foxtails, and fall panicum. These species are capable of producing large amounts of seed if allowed to reach maturity, and these are seeds that will contribute to weed-control issues in future growing seasons.

Farmers have several options available to control weeds in wheat stubble fields, including mowing, tillage, and herbicides. To achieve the highest level of success, these options should be implemented before the weeds begin to produce seed.

Mowing can effectively reduce the amount of weed seed produced by established broadleaf weeds. 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 weed seed might still be produced from plants that regrow or from tillers present on grasses below the height of cutting. This method can help reduce seed production of simple perennials (such as common pokeweed) but would do less to contain the expansion of perennial species that spread primarily by underground rootstocks (such as Canada thistle and johnsongrass).

Tillage is a viable option to control weeds in wheat stubble. Large weeds may be more effectively controlled with an "aggressive" tillage implement (such as a tandem disk) compared with a less-aggressive implement (such as a field cultivator). While effective at controlling established weeds, keep in mind that tillage can stimulate germination and emergence of additional weeds. Consumption and cost of fuel and 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 present in wheat stubble fields. Herbicides such as glyphosate, 2,4-D, and dicamba are examples that can be applied alone or in combination to control weeds in wheat stubble fields. Be sure to refer to the respective product labels for application information, such as rates, additives, rotational intervals, and so on. As always, precautions should be taken to reduce drift (movement of spray particles or vapor movement) from the target area.--Aaron Hager and Dawn Nordby

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