Influence of gender and glyphosate resistance on Palmer amaranth growth and interference with cotton

Management of herbicide-resistant weeds can be improved by understanding the biology of resistant biotypes. While the majority of research has focused on female plants and seed production of Palmer amaranth (Amaranthus palmeri S. Watson) that are resistant to glyphosate, growth of male plants that are resistant to this herbicide has not been studied in detail. Additionally, interference of male versus female Palmer amaranth plants on cotton (Gossypium hirsutum) yield has not been reported. Plant height and biomass of male and female plants from a mixed population of glyphosate-resistant (GR) and glyphosate-susceptible (GS) plants was studied in North Carolina when grown season-long with cotton. Palmer amaranth height was less for GR male plants compared with GS males and both GR and GS females. Biomass of Palmer amaranth female plants was twice that of male plants irrespective of glyphosate resistance. Cotton yield was affected similarly by Palmer amaranth regardless of either gender or glyphosate resistance status. The implications of shorter GR male plants on pollen dispersal and ramifications on management of glyphosate resistance are not known. Results from these trials did not address implications of the height of male plants on fitness of GR resistance. Nonetheless, the finding that GR male plants were shorter in the field than GS male plants warrants a new look at this topic. Similar reductions for cotton yield in presence of both GR and GS biotypes and genders suggest that current yield loss assessments and management decisions do not need to consider these variables in Palmer amaranth populations. Understanding the biology of Palmer amaranth (Amaranthus palmeri S. Watson) plants that are glyphosate-resistant and glyphosate-susceptible can facilitate improved management of this weed in crops. Research in North Carolina found that glyphosate-resistant male plants were shorter than glyphosate-susceptible male plants. Cotton (Gossypium hirsutum L.) yield was affected the same regardless of gender or susceptibility to glyphosate even though female plants exhibited twice the biomass of male plants. Further research is needed to address the impact of shorter male plants that are glyphosate resistant on pollen movement and possible fitness of this weed associated with herbicide resistance. These results also indicate that management decisions for Palmer amaranth do not need adjustment based on gender or glyphosate resistance relative to interference with cotton yield.