Competition Between Annual Weeds and Sweet Spanish Onions

The competitiveness of annual weeds in irrigated sweet Spanish onions ( Allium cepa L.) was studied at North Platte, Nebraska, during 1969 and 1970. Weeds allowed to grow in the row for 2, 4, 6, and 8 weeks after onion emergence reduced onion yields 20, 20, 40, and 65%, respectively. When plots were kept weed-free until onion emergence and 2, 4, 6, 8, 10, and 12 weeks after emergence, onion yields were reduced 100, 99, 87, 75, 46, 25, and 5%, respectively. Redroot pigweed ( Amaranthus retroflexus L.), kochia ( Kochia scoparia L.), and grass weeds accounted for 54, 21, and 21%, respectively, of the total weed yield.