Evaluating Pesticide Strategies and Spray Technology Across Diverse Southern U.S. Row Crop Systems

Abstract

Effective weed management and pesticide application are crucial to achieving optimal productivity of economically important crops in the southern U.S., such as corn (Zea mays), soybean (Glycine max), and cotton (Gossypium species). This dissertation evaluates strategies to optimize herbicide efficacy and application techniques while integrating technologies to address new challenges in weed management and crop protection. Gramineous weeds, such as crabgrass (Digitaria sanguinalis) and Texas panicum (Panicum texanum), pose significant challenges in crop systems, especially those without herbicide-tolerant traits like peanuts. A field study evaluated the efficacy of herbicide options targeting these species at two critical timings: preemergence and postemergence. Preemergence herbicide applications provided up to 94% of crabgrass control, while Texas panicum was more challenging to control. Pyroxasulfone plus carfentrazone provided consistently superior control for Texas panicum, as confirmed through normalized difference vegetation index (NDVI) and biomass measurements. Postemergence applications showed that application timing significantly influences the level of control. Early applications proved most effective, particularly for the Texas panicum, with glyphosate maintaining efficacy even at lower rates across both growth stages tested. Overall, these results highlight the importance of timely herbicide application for effectively managing a broad range of gramineous weeds. Volunteer peanuts in cotton-peanut rotations have become a challenge as they can act as weeds and reservoirs for disease and insects. Isoxaflutole, applied alone or in a mixture with dicamba and fomesafen, provided high levels of volunteer peanut control, with the greatest levels of activity observed at higher rates. Due to isoxaflutole residual activity, it can be highly effective against large-seeded broadleaf weeds. It offers a promising solution for managing volunteer peanut control in cotton with isoxaflutole-tolerant traits. New approaches to applying pesticides, including sprayer unmanned aerial vehicles (UAVs), raise concern regarding potential crop injury due to the ultra-low volume used in this application compared to traditional practices. This study aimed to evaluate soybean injury from low-volume applications by UAV and ground sprayer applications at different spray volumes. Overall, higher spray volumes correlated to higher injury, likely due to greater chemical coverage and distribution on soybean leaves. Significant differences in soybean heights were observed 7 days after treatment (DAT), with the lowest height recorded in treatments where fomesafen was applied via ground sprayer at a spray volume of 47 L ha-1. In conclusion, spray applications with ultra-low volume did not result in more injury than traditional application methods. However, questions regarding weed control efficacy remain. In tall crops like corn, mid-season aerial applications with UAVs were compared with fixed-wing airplanes regarding the assessment of spray deposition and canopy penetration. UAVs gave an equal or better performance, while propeller downdraft enhanced canopy penetration. When drift-reducing agents (DRAs) were added to the tank mixture, deposition under windy conditions was improved, thus supporting the feasibility of UAVs as an alternative to conventional methods in applying fungicides in tassel-stage corn. Overall, these studies provide important insights to enhance weed management and a comprehensive use of new application technologies to improve crop protection targeting specific challenges encountered by growers in southern U.S.