Date of Graduation

12-2014

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Jason Norsworthy

Committee Member

Nathan Slaton

Second Committee Member

Larry Purcell

Third Committee Member

Michael Popp

Fourth Committee Member

Robert Scott

Keywords

Glufosinate-resistant, Glyphosate-resistant, Palmer Amaranth, Soybean

Abstract

Herbicide-resistant Palmer amaranth is the most troublesome weed in Arkansas row crops, causing producers to rely heavily on multiple mechanisms of action to reduce selection pressure for further evolution of herbicide resistance and to successfully produce a profitable crop. It is critical for the sustainability of weed management not only to adequately control this weed but also to reduce the soil seedbank using both non-chemical and chemical practices. Studies were conducted to determine the effect of soybean row spacing, seeding rate, and herbicide program on Palmer amaranth emergence, survival, and seed production in soybean, the effect of drill-seeded soybean population on Palmer amaranth emergence with and without a residual preemergence (PRE)-applied herbicide, and the impact of integrating cover crops and deep tillage with herbicide programs for glyphosate-resistant Palmer amaranth control in glyphosate- and glufosinate-resistant soybean. Herbicide application timing and choice of herbicide had more of an impact on Palmer amaranth control than either row spacing or seeding rate and greater control was observed in PRE plus postemergence (POST)-applied residual programs compared to POST-only residual programs, regardless of seeding rate and row spacing. Narrow-row soybean reached 95% canopy formation quicker than plants in wide rows, in turn resulting in greater suppression of Palmer amaranth emergence. In drill-seeded soybean, a PRE-applied residual herbicide was more beneficial in reducing Palmer amaranth emergence than increasing soybean density. Using a combination of cover crop and deep tillage along with the addition of a PRE followed by POST-applied residual herbicide program, Palmer amaranth was effectively controlled throughout the season with limited weed seed return to the soil seedbank in both glufosinate- and glyphosate-resistant soybean. Overall, herbicide programs were the strongest factor influencing Palmer amaranth control; however, the addition of a cover crop, deep tillage, and narrow row spacing play a vital role in reducing selection pressure on herbicides, thus reducing risks for new cases of herbicide resistance.

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