Purple Nutsedge (Cyperus rotundus) Control with Glyphosate in Soybean and Cotton1

Studies were conducted at the University of Florida, West Florida Research and Education Center to determine the effect of glyphosate on purple nutsedge control and nutsedge tuber production when glyphosate was applied to the same plots over 3 y in glyphosate-resistant soybean and cotton. Greater than 90% control of purple nutsedge foliage was achieved with a single POST application of glyphosate at 0.9 kg ai/ha in soybean or a sequential glyphosate application of 1.1 kg/ha POST followed by 0.6 kg/ha POST-directed in cotton. By the end of the third year of the study, these same treatments reduced purple nutsedge tuber density to less than 0.2% of the nontreated. In cotton, cultivation alone reduced tuber numbers by greater than 90%. Viability of tubers was also reduced by 80% in soybean and by 65% in cotton in the glyphosate-treated plots. Comparison treatments of imazaquin PRE followed by imazaquin POST in soybean or norflurazon PRE followed by cyanazine plus MSMA POST-directed in cotton also reduced purple nutsedge tuber density by ≥85% after three consecutive years of treatment.Nomenclature: Cyanazine; glyphosate; fluometuron; imazaquin; MSMA; norflurazon; pendimethalin; purple nutsedge, Cyperus rotundus L., #3 CYPRO; cotton, Gossypium hirsutum L. ‘Delta Pine 5415 RR’; soybean, Glycine max L. ‘Hartz 7555RR’.Additional index words: CYPRO, transgenic cotton, cultivation, purple nutsedge population dynamics.Abbreviations: DAP, days after planting; POST-directed, postemergence directed; Early-POST, early postemergence.