BEST MANAGEMENT PRACTICES TO COMBAT EVOLUTION OF HERBICIDE-RESISTANT WEEDS IN HERBICIDE-RESISTANT COTTON AND SOYBEAN. J. K. Norsworthy*1, S. M. Ward2, D. R. Shaw3, R. Llewellyn4, R. L. Nichols5, T. M. Webster6, K. W. Bradley7, G. Frisvold8, S. B. Powles9, N. R. Burgos1, W. Witt10, M. Barrett10; 1University of Arkansas, Fayetteville, AR, 2Colorado State University, Fort Collins, CO, 3Mississippi State University, Mississippi State, MS, 4CSIRO, Adelaide, Australia, 5Cotton Incorporated, Cary, NC, 6USDA-ARS, Tifton, GA, 7University of Missouri, Columbia, MO, 8University of Arizona, Tucson, AZ, 9University of Western Australia, Crawley, WA, Australia, 10University of Kentucky, Lexington, KY (313)


Best management practices (BMPs) that mitigate the risks of herbicide-resistant weeds evolving in cotton and soybean are generally no different than those recommended for other crops.  Best management practices that should be emphasized in these and other crops include: 1) an understanding of the biology of the weeds present, 2) start with clean fields at planting, overlaying residual herbicides, 3) scout fields routinely, 4) use multiple herbicide modes of action that are effective against the most troublesome or resistant-prone weeds, 5) apply a full labeled herbicide rate at the recommended weed size, 6) emphasize cultural and mechanical practices, 7) prevent weed seed production, 8) prevent field-to-field and within-field movement of weedy propagules, 8) prevent an influx of weeds from field borders, 9) manage weed seed at harvest or post-harvest, 10) use a diversified approach focused on reducing the soil seedbank.  Diversity of management practices, which has been lacking in most U.S. cotton and soybean production systems, is the key to having a long-term successful weed management program.  No doubt, these BMPs will increase weed management costs; however, they are essential to ensuring sustainable weed management and crop production, particularly low soil seedbank densities.  Unfortunately, many of these BMPs were not used by producers of glyphosate-resistant crops in the Midsouth until herbicide-resistant weeds became present.  Reactive adoption of these BMPs is occurring in the Midsouth as a result of wide-spread glyphosate resistance in Palmer amaranth.  Hopefully, lessons learned as a result of glyphosate resistance in this region can be employed to preserve the effectiveness of glyphosate in other regions.