Competition Between Purple Nutsedge and Vegetables

Competition studies were conducted in Brazil during 1972 and 1973 between high populations (160 plants/0.1 m2at 5 to 7 weeks after planting) of purple nutsedge (Cyperus rotundusL.) and the following vegetable crops: garlic (Allium sativumL. ‘Mineiro’), okra (Hibiscus esculentusL. ‘UFV 1152’), carrot (Daucus carotaL. ‘Nantes’ and ‘Kuroda’), bush-type green bean (Phaseolus vulgarisL. ‘Topcrop’), cucumber (Cucumis sativusL. ‘Aldai’), transplanted cabbage (Brassica oleraceaL. var. capitata ‘Louco’) and transplanted tomato (Lycopersicon esculentumMill. ‘Santa Rita’). Purple nutsedge grew all year with irrigation, although growth was greater during the warm, wet season (October to March). Crop losses due to purple nutsedge competition during the entire cropping season were as follows: garlic 89%; okra 62%; two carrot cultivars, ‘Kuroda’ and ‘Nantes’ 39% and 50%, respectively; green bean 41%; cucumber 43%; cabbage 35%; and tomato 53%. Critical periods of purple nutsedge competition occurred between 3 and 13 weeks for garlic; 3 and 7 weeks for okra, cucumber and the carrot cultivar ‘Nantes’; 3 and 5 weeks for tomato and the carrot cultivar ‘Kuroda’; and at approximately 4 weeks for cabbage and green bean. Purple nutsedge competed for light in the slow-growing, non-competitive crops and for nutrients in all crops. Competition for water was reduced because the vegetables were irrigated regularly. The rate of leaf area development for a competitive crop, green bean, was similar to the rate for purple nutsedge, whereas the rate was much lower for the non-competitive okra.