No. 19 Article 4/August 3, 2007

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-crop soybean after wheat harvest, hoping 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 robust "crop" of summer annual (and sometimes perennial) weed species. Unlike double-crop soybean, farmers should not allow these plants to reach maturity and produce seed.

Frequently, 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 seeds will contribute to weed control issues in future growing seasons.

Farmers have several options available to control weeds present in wheat stubble fields, including mowing, tillage, and herbicides. To achieve 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. This method can help reduce seed production of simple perennials (such as common pokeweed), but it would do less to contain the expansion of perennial species that can spread 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 one (such as a field cultivator). While tillage is effective at controlling established weeds, keep in mind that it can stimulate germination and emergence of additional weeds. Fuel consumption/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. Herbicides such as glyphosate, 2,4-D, and dicamba are examples that can be applied alone or in combination. Be sure to refer to the respective product labels for application information, such as rates, additives, rotational intervals, and the like. As always, precautions should be taken to reduce driftmovement of spray particles or vaporfrom the target area.--Aaron Hager

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