Date of Graduation

5-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Crop, Soil & Environmental Sciences (PhD)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Norsworthy, Jason K.

Committee Member

Butts, Thomas R.

Second Committee Member

Nalley, Lawton L.

Third Committee Member

Vazquez, Alan

Fourth Committee Member

Drescher, Gerson L.

Keywords

Cotton; Herbicide; Machine vision; Palmer amaranth; Soybean; Targeted applications

Abstract

Row crop producers across the southern United States are observing a boom in technological advancement to improve operational efficiency. Additionally, environmental concerns and reduced profit margins drive the adoption of targeted pesticide application technologies like the John Deere See & Spray. This technology is relatively new, introduced in 2022, and producers need more insight into the shortcomings, potential herbicide savings, and the economic benefits of adoption. Since 2021, research has been conducted in Keiser, AR, with additional collaborative projects in Mississippi, North Carolina, Indiana, and Illinois. Five different objectives were addressed in this research: 1) to determine the impact of residual herbicide application methods in soybean [Glycine max (L.) Merr.]; 2) to evaluate targeted application (TA) performance in cotton (Gossypium hirsutum L.) grown with and without cover crops; 3) to quantify the likelihood of treating weeds with TA while considering the dynamics between weeds, crops, and detection settings; 4) to assess the ecological risk of adopting TA at two extreme detection settings in a three-year soybean system; 5) to quantify the opportunity cost between traditional broadcast applications and targeted sprayer systems. The first objective evaluated either TA of all herbicides (single-tank), TA of postemergence (POST)-active herbicides and broadcasting residual herbicides (dual-tank), and different residual application timings in four site years. Targeted applications provided comparable control to traditional broadcast applications across all weeds, resulting in a 28.4% to 62.4% POST herbicide savings. The second objective evaluated single-tank TA, dual-tank TA, and broadcast applications in fallow, cereal rye (Secale cereale L.), or hairy vetch (Vicia villosa Roth] cover crop systems. Overall, TA with See & Spray could detect weeds in cover crop biomass. By the end of the season, weed control for all species, including Palmer amaranth (Amaranthus palmeri S. Watson), was ≥ 92%. For Objectives 3 and 4, the lowest sensitivity settings reduced the likelihood of treating weeds, with Palmer amaranth < 5cm in height being missed 39% of the time with the lowest setting, which ultimately caused an increase in weed density in subsequent years. For areas treated using the lowest sensitivity each year, the weed density increased from 867 weeds ha-1 in 2022 to 11,300 weeds ha-1 in 2024, while plots containing the high sensitivity and broadcast treatments had 2,336 weeds ha-1 at termination in 2024. For the opportunity cost, nozzles with narrower spray plume angles sprayed less, and average break-even points were determined for a John Deere 412R (Deere & Company, Moline, IL) when purchasing a new or upgrading an existing sprayer. Adopting See & Spray appears to be a viable tool to reduce the environmental loading of herbicides and enhance producer profitability if appropriately utilized. Within a program approach, targeted applications can provide comparable weed control to broadcast applications with a medium or higher sensitivity setting. Reduced weed areas improve targeted herbicide savings and emphasize the importance of highly effective residual herbicide programs and integrated weed management strategies. Lower sensitivity settings increased Palmer amaranth density in subsequent years and should not be utilized for typical herbicide applications. Return on investment will depend heavily on the investment cost, intended herbicide program cost, and weed densities at the time of application.

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