Density Effect and Economic Threshold of Purple Nutsedge ( Cyperus rotundus L.) in Peanut ( Arachis hypogaea L.)

Peanut is one of the most important oilseed crop grown in China. Purple nutsedge ( Cyperus rotundus L.) is a competitive perennial weed, which infests peanut fields in south China and causes considerable peanut yield losses. Information on the interference of purple nutsedge on peanut and its economic threshold (ET) in field is an integral component of integrated weed management system. This will help growers use herbicides more legitimately and reduce the amount of herbicide that is discharged into the environment. 2-year experiments were conducted to assess the infestation effects of purple nutsedge on peanut in pure stands (nutsedge density 0, 5, 10, 20, 40, 80, 120 and 160 plants m −2 ) and in natural weed infestation, respectively. Furthermore, the ET of purple nutsedge in peanut was determined according the quadratic equation reported by Cousens. The biomass of purple nutsedge with a density of 160 plants m −2 in pure stand was less than that of natural weed infestation treatment. Compared with natural weed infestation treatments, lower yield loss in treatment of nutsedge 160 plants m −2 indicated weaker interference on peanut. But the ET of purple nutsedge in peanut came down to 4–5 plants m −2 . The higher price of peanut than the cost of weed control and very high efficiency (90%) of imazapic could be the probable reasons.