Date of Award

5-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Committee Member

Dr. Michael W. Marshall, Committee Chair

Committee Member

Dr. Jeremy Greene

Committee Member

Dr. Todd Campbell

Abstract

To evaluate weed management programs in cotton tolerant to dicamba and 2,4-D, field experiments were conducted in 2011, 2012 and 2013 at the Edisto Research and Education Center near Blackville, South Carolina. The studies addressing herbicide programs in cotton tolerant to dicamba consisted of different herbicide combinations sprayed at different timings. Some programs included a PRE with multiple POST applications and some did not include a PRE and were POST only. In each study, the dicamba herbicide treatments provided excellent control (95 to 100%) of Palmer amaranth and pitted morningglory throughout the growing season, which reduced competition and protected overall yields. Control of large crabgrass was more variable between studies. Treatments applied at PRE and POST 1 resulted in high seed cotton yields because the cotton plants did not have any competition at the critical growing stage of cotton, 8 - 10 weeks after planting. There was no crop injury observed from applications of dicamba or 2,4-D. The studies addressing herbicide programs in cotton tolerant to 2,4-D included PRE and POST treatments, and excellent control of Palmer amaranth was observed by all treatments in each study, with the exception of a no PRE and glyphosate alone POST 1 and 2 herbicide program having 88% control. In 2011 and 2012, 2,4-D choline plus glyphosate and glufosinate provided excellent control of pitted morningglory, and in 2013 the herbicides provided a range of 80 to 95% control. In 2011 and 2012, yields were high across all treatments due to adequate weed control and growing conditions. Yield was extremely low in 2013 because of excessive early rainfall events, water-soaked fields, and late planting dates. In greenhouse experiments evaluating the control of grass species at various height intervals with combinations of dicamba, glyphosate, 2,4-D, and glufosinate combinations using three different nozzle types, large crabgrass and broadleaf signalgrass were controlled at heights from 5 to 20 cm; at 41 cm grasses were not controlled as effectively. At 41 cm percent controls ranged from 71 to 75% for large crabgrass and 84 to 89% for broadleaf signalgrass. There was no significant difference in efficacy between nozzle types.

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