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A glyphosate-based herbicide is no longer effective when it comes to managing resistant weeds such as Palmer amaranth and marestail in Mid-South cotton fields. To manage resistant weeds, growers are moving into a more systems based approach, which includes residual herbicides, crop rotation, tillage and hand weeding. Darrin Dodds, Mississippi State University Extension Cotton Specialist, discusses obstacles growers must overcome to achieve maximum yield potential during a recent interview.
Question: What are the major problem weeds in your area?
DD: The biggest one throughout the Mid-South would be glyphosate resistant Palmer amaranth. We’ve been dealing with it for a number of years now and it’s our primary problematic weed. There are some areas in Mississippi where Palmer amaranth has not yet been confirmed, but it’s probably present in those areas. We’ve also been dealing with glyphosate resistant marestail for going on 10 years, although it is not as big of a problem as resistant Palmer amaranth. We have several other weed species in Mississippi with confirmed resistance to glyphosate including Italian ryegrass; however, the previously mentioned species are especially problematic.
Question: What are the possible effects of allowing weed escapes?
DD: Weed escapes create problems because the ones that escape contribute additional seeds to the soil seedbank. This is especially true when dealing with glyphosate resistant Palmer amaranth. Each weed can produce up to 300-500,000 seeds, so for every pigweed that escapes many weeds may start to emerge. The biggest thing to understand about weed escapes is that they could create more problems down the road. The other thing to consider is that equipment including tractors, sprayer, tillage equipment, and harvest equipment can disperse pigweed and other seeds to other fields, making the problem worse.
Question: When giving advice on control, what is the first step you communicate to growers?
DD: For an effective weed management plan, I tell my growers they need to have a willingness to change what they’re doing. There was a time when growers were only using glyphosate to manage weeds in a variety of crops. That won’t work anymore. We’ve been encouraging growers to put out multiple residual herbicides throughout the course of the growing season. I’d recommend applying paraquat (Gramoxone® Herbicides, etc.) tankmixed with Cotoran® 4L Herbicide immediately after planting. Prior to emergence, the paraquat will help maintain a clean field while the Cotoran® 4L Herbicide is there for residual control. Once the crop has emerged, we recommend the use of metolachlor or s-metolachlor (Dual Magnum® Herbicide, etc.) with broadcast applications followed by an additional residual in a layby application.
Question: Where do you see the future of weed control if we continue on our current path?
DD: The future of weed control will continue to be trait-based for the foreseeable future. I think it will be trait-based given the number of new herbicides/modes-of-action I have seen in the last ten years. Although additional traits are being developed, it is important to remember that these traits should be incorporated into a complete system approach, which will include crop rotation, tillage, residual chemistry, and hand weeding where necessary.
A systems-based approach is key when controlling many of the resistant weeds that plague cotton fields throughout the Mid-South. It is critical to spot these weeds and begin treating before they reach a height of four inches, as well as hand weeding to avoid weed escapes. For additional crop recommendations, visit roundupreadyPLUS.com.
Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible.10;10; ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Roundup Ready PLUS® is a registered trademark of Monsanto Technology LLC. Deltapine® is a registered trademark of Monsanto Company. Gramoxone® is a registered trademark of a Syngenta group company. All other trademarks are the property of their respective owners. Cotoran® is a registered trademark of Makteshim-Agan of North America, Inc. ©2013 Monsanto Company.