Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2003
Publication Date: 1/1/2004
Citation: Anderson, R.L. 2004. Sequencing crops to minimize selection pressure for weeds in the semiarid great plains. Weed Technology 18: 157-164. Interpretive Summary: Producers in the Central Great Plains are diversifying their crop rotations by adding corn, sunflower, or proso millet to winter wheat-fallow. This diversity in crops may help producers in managing weed populations in their fields. To explore this possibility, we conducted a life cycle simulation based on jointed goatgrass and green foxtail population dynamics to estimate impact of crop sequencing on weed community density. Our results show that arranging crops in a cycle of four, with two cool season crops followed by two warm season crops, can reduce selection pressure for weeds 200,000- to 600,000-fold. Varying crops with different planting dates within a life cycle interval, such a warm season crops, is crucial for ensuring that weed population growth does not occur. Designing rotations based on this strategy will help producers in developing alternative weed management strategies as well as improving effectiveness of herbicides used and minimizing herbicide resistance.
Technical Abstract: Rotations are changing in the semiarid Great Plains because of no-till systems. Producers now rotate summer annual crops such as corn with winter wheat and fallow, which can disrupt weed population growth because of diverse life cycles among crops. This study estimated changes in weed populations as affected by rotation design, with the goal of suggesting crop sequences that lower weed community density. We used an empirical life cycle simulation based on demographics of jointed goatgrass and green foxtail, to compare various rotations comprised of winter wheat, corn, proso millet, and/or fallow across a 12-yr period. The simulation indicated that designing rotations to include a 2-yr interval where seed production of either jointed goatgrass or green foxtail is prevented will drastically reduce weed populations. Arranging four different crops in sequences of two cool season crops followed by two warm season crops was the most beneficial for weed management. Selection pressure for weeds among rotations varied almost 600,000-fold for jointed goatgrass and 200,000-fold for green foxtail. Fallow, if used, serves in either life cycle category. Impact of rotation design on weed density was further enhanced by improving crop competitiveness with cultural practices. Devising ecologically-based rotations not only reduces weed density, but enables producers to use alternative weed management strategies, improve effectiveness of herbicides used, and minimize herbicide resistance.