Evaluation of Integrated Weed Management and Herbicide Tolerance in Peanut-Cotton Rotation
Type of DegreePhD Dissertation
Crop Soils and Environmental Sciences
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As resistant weeds such as Palmer amaranth (Amaranthus palmeri L.) continue to spread through the Southeast, peanut-cotton producers are forced to utilize herbicides which pose a greater risk to injuring crops to control weeds. Peanut producers are further limited by the number of labeled herbicides available. Evaluating alternative non-chemical weed control methods utilizing cover crops is imperative for the future of peanut production. A series of field experiments were designed to assess peanut and cotton tolerance to select herbicides known to cause injury and to evaluate integrated weed management utilizing cover crops with residual herbicides. The first study evaluated peanut tolerance to evaluate the effect of PPO-inhibitor herbicide treatments on dryland peanut growth and yield when applied during reproduction stages: 60 (R4-R5), 75 (R6), and 90 days (R6-R7) after planting as well as combinations with different surfactants. Treatments including high surfactant oil concentrate were more likely to cause injury and yield loss than those with non-ionic surfactants. Treatments applied at 75 days after planting (DAP) were more likely to cause yield loss than those applied at 60 to 90 DAP. The second study evaluated the effect of paraquat based herbicide programs on newer peanut cultivars growth and yield. Data indicated peanut stunting may be observed following applications of paraquat tank mixes evaluated in this study, but it is unlikely these effects result in yield loss. The third study evaluated sensitive cotton stunting and yield responses resulting from 2,4-D or dicamba residues in soil after preplant burndown applications at 3 weeks prior to planting and day of planting. The data suggests stunting and stand reduction may occur if susceptible varieties are planted soon after burndown applications with 2,4-D or dicamba, but yield may not be affected after a full growing season. Dicamba showed greater potential to cause stunting and stand reduction than 2,4-D. Incorporating cover crops has shown to help reduce weed emergence and pressure along with providing many additional agronomic benefits. However, residual herbicides can affect fall seeded cover crop establishment reducing weed suppressive qualities. The objective of the fourth trial was to investigate the responses of six cover crops (daikon radish, cereal rye, oat, crimson clover, winter wheat, and common vetch) to 12 soil residual herbicides commonly used in peanut-cotton rotation. Overall, no significant biomass reductions were observed for any cover crop species, with oats showing the most tolerance with no treatments reducing any growth parameters evaluated. Although initial injury and stunting may occur, biomass at termination of cover crops were not affected by herbicide residues evaluated in this study. As more farmers utilize no till or minimum tillage practices, previous herbicide programs need to also be evaluated to determine if they are still effective or necessary for early season weed control. Cover crop residues could prevent residual herbicides from reaching the soil surface, allowing weeds to germinate where there are gaps in the residues. The objectives of this trial were to (1) evaluate the effectiveness of residual herbicides on weed control in conventionally tilled versus high cover crop residue systems, (2) determine if weed control was greater with the combination of cover crops and residuals herbicides compared to conventionally tilled systems. Overall, combinations of heavy cover crop residue and residual herbicides provided better weed control than conventionally tilled systems. There was 75 to 89% less weed biomass with combined high residue and residual herbicides compared to conventional tilled non-treated check. These data suggest the residual is still reaching the soil surface and providing additional wed control. Finding alternative and integrated weed management programs that include agronomic practices, cover crop residues, and herbicide programs is key to the future of peanut production.