Economic assessment of new weed management technologies in strip- and conventional-tillage cotton and peanut and common ragweed interference in peanut

by 1972- Clewis, Scott Barton

CLEWIS, SCOTT BARTON. Economic Assessment of New Weed Management Technologies in Strip- and Conventional-Tillage Cotton and Peanut and Common Ragweed Interference in Peanut. (Under the direction of Dr. John W. Wilcut). Low commodity prices and environmental concerns have compelled cotton growers to increase production efficiency while decreasing inputs. Research evaluated weed interference, strip-tillage production, transgenic cultivars, and new herbicides to improve weed management in peanut and cotton. The rectangular hyperbola model described the effect of common ragweed density on percent peanut yield loss. With the asymptote constrained to 100% maximum yield loss, the I coefficient (yield loss per unit density as density approaches zero) was 68.3 + 12.2%. Common ragweed height was not affected by weed density or peanut canopy diameter. Weed height exceeded peanut height throughout the growing season, indicating that competition for light occurred between the two species. Common ragweed above-ground dry biomass per plant decreased as weed density increased, but total weed dry biomass per m crop row increased with weed density. Studies evaluated weed management using diclosulam and flumioxazin in striptillage and conventional-tillage peanut. Dimethenamid plus diclosulam or flumioxazin preemergence (PRE) controlled common lambsquarters, eclipta, and prickly sida at least 91%. Diclosulam and flumioxazin controlled Ipomoea morningglory species (59 to 91%) and bentazon plus acifluorfen postemergence (POST) provided > 90% control. Dimethenamid plus diclosulam or flumioxazin PRE produced equivalent yields and net returns with no significant differences between the two PRE options. The tillage production system did not influence weed control of eight weeds, peanut yields, or net returns. Studies were conducted to evaluate weed management systems in nontransgenic, transgenic bromoxynil-resistant, and transgenic glyphosate-resistant cotton in strip- and conventional-tillage environments. Tillage did not affect the level of weed control provided by the herbicide systems evaluated. Excellent ( > 90%) control of common lambsquarters, Ipomoea species including entireleaf, ivyleaf, pitted, and tall morningglories; jimsonweed, prickly sida, and velvetleaf was achieved with programs containing bromoxynil, glyphosate, and pyrithiobac early postemergence (EPOST). Glyphosate systems controlled fall panicum, goosegrass, and large crabgrass more consistently than bromoxynil and pyrithiobac systems. Bromoxynil and pyrithiobac