Management of Purple Nutsedge (Cyperus rotundus L.) Tuber Populations in Rice-Onion Cropping Systems

A high tuber population in rice-vegetable cropping systems makes purple nutsedge (Cyperus rotundus L.) difficult to control because of tuber dormancy and longevity. Studies were conducted to quantify production and population dynamics of tubers of purple nutsedge growing alone or in a rice-onion rotation system managed with strategies that reduce tuber production (herbicides and handweeding) or tuber survival (stale-seedbed technique). In pot studies, one purple nutsedge plant produced 550 tubers and 375 shoots after 4 mo. In field studies, an initial density of 1 tuber/m2 increased to an average of 1200 tubers/m2 within 3 months from planting, declined by 50% after the first crop and by 95% after the fourth crop, with tuber longevity of 17 mo. Tuber populations in treated plots decreased faster, and were lower, than those in nontreated plots after three cropping seasons. The decline in tuber and shoot populations in plots treated with herbicides and handweeding was immediate, but not as long-lasting as that in plots treated with stale-seedbed. Although crop yields were comparable, weed control costs were lower by 15-70% and net incomes were higher by 15% in stale-seedbed than in herbicide or handweeding treatments, indicating their greater cost-effectiveness over the latter treatments. Key Words: Cyperus rotundus, population dynamics, stale-seedbed, tillage