Purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.) management with tillage and the herbicides imazapic and imazethapyr

Purple and yellow nutsedge (Cyperus rotundus L. and C. esculentus L.) together, rank fifth in importance among all weeds in the United States. Both of these nutsedge species reduce peanut ( Arachis hypogaea L.) yields by competing for water, light, and nutrients. They also reduce crop quality due to the contamination of harvested peanuts by nutsedge tubers. Due to the prolonged use of herbicides that differentially controlled yellow nutsedge, purple nutsedge has become an even greater problem in southeastern peanut fields. Imazapic (Cadre) and imazethapyr (Pursuit) were the first herbicides to provide effective postemergence purple nutsedge control in peanuts.;Field and greenhouse studies were conducted to determine the effectiveness of imazapic and imazethapyr in controlling purple and yellow nutsedge, and to evaluate the impact these herbicides have on nutsedge tuber production. Tillage was also evaluated as a means of reducing purple nutsedge growth and reproduction. Tilling at two week intervals more than twice in May and June did not result in significantly lower purple nutsedge tuber numbers in July.;Tilling at two week intervals more than three times throughout the season did not significantly reduce tuber numbers by September. Alternating tillage operations with glyphosate applications resulted in the greatest reduction in tuber number, weight, and viability at mid- and late-season sampling dates. In an herbicide screening study conducted for both purple and yellow nutsedge in the field, imazapic applied at the rate of 71g ha−1 early postemergence (EPOST) resulted in the greatest reduction of tuber numbers and tuber dry weights by July and September.;Greenhouse studies indicated that EPOST applications of imazapic and imazethapyr 2 weeks after emergence (WAE) were more effective than those applied to purple and yellow nutsedge 4 and 6 WAE. Foliar-only treatments of purple and yellow nutsedge 2, 4, and 6 WAE provided better shoot control than soil-applied treatments. The greatest control of nutsedge, however, regardless of plant age, was obtained by treating both the foliage and soil. It was determined at the conclusion of a year-long greenhouse study that soil-applied imazapic provided better residual control of purple nutsedge than imazethapyr.