Date of Graduation

8-2024

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Norsworthy, Jason K.

Committee Member

Barber, L. Tom

Second Committee Member

Thrash, Benjamin C.

Third Committee Member

Roberts, Trenton L.

Keywords

Cotton; Herbicide-coated Fertilizers; Palmer amaranth; Residual herbicide

Abstract

Cotton (Gossypium hirsutum L.) production faces numerous challenges, many related to weed management. A herbicide application method that focuses on combing resources that producers already have access to, such as herbicide-coated fertilizers, could be a practical approach for addressing late-season control of Palmer amaranth (Amaranthus palmeri S. Wats) and other problematic weed species. Two main factors would potentially impact the efficiency of utilizing this method: cotton tolerance to the application and weed control provided by the herbicide-coated fertilizers. Some considerations could affect the efficacy of these applications, such as when the treatments are applied and when they are activated by rainfall or irrigation. Therefore, experiments were conducted to 1) understand cotton tolerance to herbicides coated onto fertilizer, 2) evaluate the residual control of Palmer amaranth with herbicide-coated fertilizers, and 3) determine the influence of irrigation and application timing on weed control and cotton tolerance. In general, herbicide-coated fertilizer applications did not cause adverse effects on the crop, and there was no reduction in seedcotton yield was evident for any treatment. These coated fertilizer applications did not affect cotton groundcover compared to the nontreated check. All herbicide-coated fertilizer treatments provided at least 73% Palmer amaranth control at 28 d after treatment (DAT). While some herbicide treatments did experience a decrease in control across evaluation dates, from 14 to 28 DAT, certain treatments provided weed control that was similar at both evaluation dates, such as fluridone, fluridone plus fluometuron, pyroxasulfone, pyroxasulfone plus fluridone, and S-metolachlor. Palmer amaranth present in plots did not interfere with cotton growth and development, and no reduction in seedcotton yield occurred. Irrigation/activation timing of the herbicide-coated fertilizers can greatly impact the efficacy of the application. Control of both Palmer amaranth and barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] was decreased when irrigation was applied 10 d after application (DAA). Applying irrigation 0 or 3 DAA greatly increases herbicide activity, resulting in greater Palmer amaranth and barnyardgrass control. Florpyrauxifen-benzyl, while not labeled in cotton, did not cause more than 20% injury regardless of application timing when applied coated onto fertilizer. Many herbicides applied in this manner provide added residual Palmer amaranth control without causing adverse effects to cotton. Based on the results of these experiments, many herbicides have the potential to be integrated into cotton production systems in season coated onto fertilizers.

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