OVERCOMING AUXIN HERBICIDE ANTAGONISM USING NOVEL APPLICATION METHODS FOR GRASS WEED CONTROL IN COTTON AND SOYBEAN PRODUCTION SYSTEMS.

Our long-term goal is to effectively solve auxin herbicide antagonism of grass control herbicides through a viable on-farm solution to be widely adopted by growers across Mississippi and surrounding region. The overall objective of this project to meet the long-term goal, will be to research novel spray application methods and understanding the chemistry of why these herbicides antagonize each other to provide a feasible solution for growers. The central hypothesis for the proposed research is that applying auxin herbicides and grass control herbicides by limiting the time the two herbicides mix within the sprayer effectively overcomes herbicide antagonism for grass weed control.R1: Research Objective 1: Fine-tune the novel application methods to make them feasible at the farm level, modifying existing equipment that would prevent the grower from having to purchase a new sprayer to overcome herbicide antagonism. Preliminary data has shown that by applying the auxin and grass control herbicides through separate spray tanks and booms, herbicide antagonism can be eliminated. The goal of this objective is to improve application methods where the herbicides are applied separately and further developed to ensure that scaling them up for a commercial grower can be accomplished while overcoming the antagonism. Our working hypothesis for this objective is: applying herbicides that antagonize each other by applying them separately effectively overcomes herbicide antagonism for grass weed control. We will test our working hypothesis through our first approach by determining the effectiveness of direct-injection systems - which functions to "inject" spray lines with another herbicide, thereby reducing the time the two herbicides interact with one another. The second approach will be to optimize our proven method of applying the herbicides from separate spray tanks and spray booms to for scaling up for large scale spraying equipment and collaborate with growers through the process. The rationale under this objective is that direct injection systems are commercially available and already in use by many growers. Without the knowledge of how to utilize these proven application methods by scaling them up for use on the farm will result in continued herbicide antagonism and poor grass control, leading to millions of dollars lost from reduced cotton and soybean yield. When the proposed studies for this research objective are complete, we expect the overall outcome to yield a solution that can be readily disseminated and taught to growers through our extension objective. This result is expected to have significant value to cotton and soybean growers who can apply these solutions for all herbicide combinations for control of all major weed species where they suspect herbicide antagonism to be occurring.R2: Research Objective 2: Elucidate the type of antagonism occurring with the auxin herbicide in combination with the grass control herbicide to better develop field solutions to overcome this antagonism. Preliminary data has shown that the concentrations of the grass herbicides are significantly lower in grass samples when the auxin herbicide is tank mixed with it. The goal of this objective is to elucidate how the antagonism is occurring within the grass, to better develop solutions for reducing this in the field. Our working hypothesis for this objective is: when the auxin herbicide and the grass control herbicide are mixed in the spray solution, the antagonism that is occurring is biochemical antagonism, where one herbicide prevents the other herbicide from translocating throughout the plant to elicit biological activity. We will test our working hypothesis with our first approach by quantifying herbicide concentrations from trialed spray application methods using liquid chromatography mass spectrometry (LC/MS) - a method described in the preliminary data section by harvesting plants 24 hours after spray application and then measuring resulting herbicide concentrations. The second approach will be to partition grasses in specific areas (uppermost blades, vascular tissues, and lower canopy blades) to discern where the herbicide is reaching within the grass to further elucidate the type of antagonism occurring. The rationale under this objective is that quantifiable herbicide concentrations can allow for understanding better what type of interaction the herbicides are having with each other to answer this question. Without the knowledge of how the herbicides are antagonizing each other, addressing the method to overcome this in the field will be incomplete, and further advances in solving this problem will be stalled. When the proposed studies for this research objective are complete, we expect the overall outcome to yield the answer to the question of why and how these herbicides antagonize each other to advance a solution that can be readily disseminated and taught to growers through our extension objective. This result is expected to create a foundation on which to build further research of other known antagonistic herbicide combinations that result in poor weed control and millions of dollars lost for growers of all crops across the United States.E1: Extension Objective 1: Disseminate the information for growers to change the application method they use to apply these herbicides to result in maximum control of grass weeds in cotton and soybean. Results from the first two objectives will provide a solid foundation to deliver sound results to growers which will be of great interest to solving a major weed control problem they face. The goal of this objective is outreach with growers to show them how they can implement these application methods on their farms to overcome herbicide antagonism for grass control. Our working hypothesis for this objective is: growers will adopt novel application methods to overcome herbicide antagonism from an auxin herbicide and a grass control herbicide when feasible methods are developed at the farm level. We will test our working hypothesis with our first approach through outreach to growers in off-season extension opportunities including speaking at grower meetings, and through electronic media by collaborating with Cotton Incorporated, the United Soybean Board and eXtension to expand our outreach as widely as possible. The second approach will be to host extension field days during the early part of the growing season, and throughout the growing season. The third approach is to make on-farm visits to meet with growers on a one-on-one basis to address concerns they have as well as show them exactly how our methodology would work effectively in their production system. The rationale under this objective is that by reaching growers through multiple platforms, we can ensure our greatest outreach is achieved and that adoption of these methods maximized. Without the outreach component of this integrated project, our new-found methods and knowledge on herbicide antagonism will be stalled. When the proposed studies for this extension objective are complete, we expect the overall outcome to yield high rates of adoption by growers to improve the economic and environmental sustainability of their production systems now and in the long run. This result is expected to create a network of growers who adopt this technology and want to trial the method for application of other herbicides for which they suspect antagonism occurring, thereby creating an on-going and impactful contribution to improving weed control in southern crops.