chapter  7
20 Pages

A Rotation Design That Aids Annual Weed Management in a Semiarid Region

The predominate rotation in the Great Plains is winter wheat (Triticum aestivum L.)-fallow. Producers developed this rotation in response to the region’s semiarid climate where yearly precipitation ranges from 250 to 450 mm per year and evaporation potential approaches 1,500 mm. To compensate for these climatic limitations, producers include fallow in the rotation. During fallow, no crop is grown and weeds are controlled, thus precipitation is stored in soil. The reservoir of soil water gained during fallow improves growth of the following winter wheat, subsequently reducing yield variability and crop loss due to drought stress. In addition, producers grow sorghum [Sorghum bicolor (L.) Moench], proso millet (Panicum miliaceum L.), corn (Zea mays L.), and sunflower (Helianthus annuus L.), but presently, winter wheat is the major crop of the region. Status of Current Weed Management

Producers in the Great Plains rely on a multitude of strategies to control weeds, such as tillage or cultural practices, but especially emphasize herbicides. Initially, herbicides were so effective that producers perceived them to be the “silver bullet,” controlling weeds with one management tactic. A startling consequence of this single-tactic approach, however, is the development of weeds resistant to herbicides (Holt and LeBaron, 1990). In the Great Plains, herbicide-resistant weeds such as downy brome (Bromus tectorum L.), Russian thistle (Salsola iberica Sennen & Pau), and kochia [Kochia scoparia (L.) Schrad.] are now common (Lyon, Miller, and Wicks, 1996).