Long‐term Management of Palmer Amaranth with Herbicides and Cultural Practices in Cotton

Abstract

Core Ideas Deep tillage reduced Palmer amaranth populations Hand‐removal of Palmer amaranth over 4 yr reduced the soil seedbank and maintained a low frequency of glyphosate resistance Hand‐removal of Palmer amaranth was more effective than deep tillage in preventing an increase in glyphosate resistance Glyphosate‐resistant (GR) Palmer amaranth (Amaranthus palmeri S. Watts) has become one of the most problematic weeds in cotton (Gossypium hirsutum L.) production systems throughout the southern United States. Research was conducted from 2012 through 2015 in continuous cotton to determine the influence of a single deep tillage operation and annual hand‐removal of Palmer amaranth plants prior to seed production on weed populations, cotton yield, and economic returns when a commercial standard herbicide program was implemented each year. Treatments consisted of both a one‐time deep tillage operation in fall of 2011 and no deep tillage, each with and without annual hand‐removal of Palmer amaranth. The single deep tillage operation reduced Palmer amaranth populations 75% during the 2013 growing season. Differences in weed populations with deep tillage did not always translate into increased yield and economic return. After four growing seasons, cumulative economic return was not affected by deep tillage or hand‐removal. However, hand‐removal of Palmer amaranth plants prior to seed production each year resulted in a lower density and a lower frequency of glyphosate resistance after 4 yr.