Date of Award

8-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Plant and Environmental Science

Committee Chair/Advisor

Dr. Michael Marshall

Committee Member

Dr. Joe M. Maja

Committee Member

Dr. June Luo

Committee Member

Dr. Gilbert Miller

Abstract

Leaf shedding is a natural process as cotton matures; however, this does not synchronize with harvest timing; therefore, defoliants are used to remove these leaves and improve harvestability of the bolls. A tractor-mounted boom sprayer is typically used to apply defoliants. However, this approach results in low penetration to the bottom canopy, poor defoliation, and, consequently, lower fiber quality. An autonomous robotic spraying system equipped with pulse width modulation technology enables targeted side-spraying of defoliants, overcoming the limitations of conventional over-the-top applications. However, limited information on staggered defoliation timing and its effect on cotton fiber quality is available. Thus, field research was conducted at two locations, Edisto Research and Education Farm (EREC), Blackville and South Carolina State Research and Demonstration Farm (SCSRDF) in Olar in 2024 to evaluate five different staggered application timing intervals (15, 10, 8, 5, and 3 days) and standard over-the-top broadcast application (60% open boll) on fiber quality. Fiber quality was measured using High Volume Instrument (HVI) and Advanced Fiber Information System (AFIS). Staggered defoliation timings influenced fiber quality parameters, especially fiber length. The upper half mean length was significantly different for staggered timings, with values ranging from 1.09 mm to 1.14 mm and 1.10 mm to 1.13 mm at EREC (p=0.0791) and SCSRDF (p=0.0746), respectively. The AFIS results were also significant for L(w), UQL (w), and L5%(n) at (p< 0.0001) and L(n) (p=0.0682) at EREC. At SCSRDF, L(w) and UQL (w) were significant at p=0.0640 and 0.0717, respectively. Fiber maturity was also influenced by staggered defoliation with the 15-day interval, resulting in the lowest micronaire of 3.63 and 3.37 at EREC and SCSRDF, respectively. The 15-day intervals according to AFIS had the highest immature fiber content, which was different from 10, 5, and 3-day timings and control at SCSRDF. However, fiber fineness and maturity ratio were similar for all treatments and control at both the locations. Uniformity index (p=0.0673), reflectance (p=0.0842), trash (p=0.0468), and short fiber index (p=0.0810) were significantly different for staggered defoliation at EREC, whereas at SCSRDF strength (p=0.0822), elongation (p=0.0882), and trash area (p=0.0759) were significantly different. Results from the AFIS analysis revealed no significant differences in neps and trash parameter except for trash size at EREC (p=0.0175). These findings suggest that staggered defoliation could enhance fiber quality, fiber length, maturity and reduce trash content. Moreover, these findings emphasize the potential of autonomous robotic systems for defoliant applications and encourage the advancement of autonomous spraying technology on optimizing fiber quality by enabling targeted, canopy-specific defoliation strategies.

Author ORCID Identifier

0009-0007-2410-7485

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