Weed Management for Sustainable Cotton Production in West Texas

This research investigates the effect of commonly used herbicides and varying irrigation levels on soil health, weed management, and cotton (Gossypium hirsutum L.) productivity in the Texas High Plains over two growing seasons (2023 and 2024). The study addresses the challenges faced by cotton growers due to water scarcity from declining Ogallala aquifer levels and weed infestations, particularly by Palmer amaranth (Amaranthus palmeri S. Watson), in a semi-arid climate. By evaluating the impact of pre-emergent herbicides (trifluralin, prometryn, S-metolachlor, and acetochlor) and post-emergent herbicides (glyphosate, glufosinate, and dicamba) applied at recommended and double field rates on soil health, and by examining how different irrigation levels [100% crop evapotranspiration (ETc) and 50% ETc] affect herbicide efficacy, the research study aims to provide insights for sustainable cotton production. The results indicate that the application of these herbicides did not adversely affect soil health indicators such as soil organic matter, pH, or electrical conductivity, even when used at twice the recommended rates. Application of pre-emergent herbicides, S-metolachlor and acetochlor enhanced soil microbial biomass carbon and nitrogen, suggesting stimulation of microbial activity and maintained or increased β-glucosidase enzyme activity, which is crucial for soil carbon cycling. Regarding cotton productivity, herbicide application improved plant growth parameters, including height and biomass. Pre-emergent herbicides, particularly prometryn and S-metolachlor at higher rates, significantly increased lint and seed yield compared to untreated control and post-emergent herbicides, especially dicamba at 2x recommended rate, resulted in the highest lint and seed yield in both years. When examining the impact of irrigation levels on herbicide efficacy, the study found that reducing irrigation to 50% ETc did not significantly affect total weed density or biomass but effectively reduced the height and biomass of Palmer amaranth, a most troublesome herbicide-resistant weed. Herbicide treatments included pre-emergent herbicides followed by a tank-mix of pre-emergent and post-emergent herbicides, which were most effective in controlling weeds, such as a combination of acetochlor, prometryn or S-metolachlor, respectively, with glyphosate significantly reduced weed density and biomass compared to untreated control and sole pre-emergent application. Despite the reduction in cotton plant height under deficit irrigation, lint yield was comparable between two irrigation levels (50% ETc and 100% ETc) due to effective weed control and timely precipitation during the boll-setting stage, which mitigated the stress from reduced irrigation. The sequential herbicide application, particularly S-metolachlor and acetochlor, resulted in significantly higher lint yield than untreated control under both irrigation levels. In conclusion, the study demonstrates that the most common cotton herbicides recommended can effectively control weeds without harming soil health. It also demonstrates that deficit irrigation is a viable water-saving strategy that does not compromise cotton yield and herbicide efficacy. Farmers can enhance weed control and sustain cotton productivity in semi-arid regions facing water scarcity by integrating effective herbicide management programs with optimized irrigation practices. This research provides valuable insights for developing sustainable cotton production systems that balance effective weed management, soil health preservation, and efficient water use.