Date of Graduation

12-2015

Document Type

Thesis

Degree Name

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

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor

Jason K. Norsworthy

Committee Member

Fred Bourland

Second Committee Member

Tom Barber

Third Committee Member

Richard Norman

Keywords

Biological sciences; Cotton; Light; Palmer amaranth; Weed science

Abstract

Increasing populations of glyphosate-resistant weeds, such as Palmer amaranth, have prompted growers to pursue alternative means of weed control in cotton. In many cropping systems, this means the utilization of older chemistries and residual herbicides. The goal of this research was to evaluate and understand the agronomic and environmental factors that affect the inconsistent injury often associated with these herbicides as well as determine the impact of Palmer amaranth emergence date on seed production, biomass, and cotton yield. Experiments were conducted in three counties in Arkansas giving a distinct range of climate and soil texture. Injury, biomass, and number of plants per m of row, number of seed per female Palmer amaranth plant, and cotton yield were assessed in experiments under various conditions.

Seed vigor levels, seed size, stressed conditions, and planting depth constituted the majority of factors evaluated. Low seed vigor increased the risk of injury from diuron, fomesafen, and fluometuron. Increasing planting depth from 0.64 to 2.5 cm resulted in greater cotton injury from fomesafen but proved inconsequential when applying diuron or fluometuron preemergence. Cotton injury from glufosinate was observed on two Widestrike® cultivars and to a lesser extent on a Liberty Link® cultivar. Injury from glufosinate was significantly increased when cotton was shaded prior to application. Palmer amaranth emerging for the 10-week period after cotton emergence is capable of producing seed, which points to need for extended period of weed control in cotton.

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