THE CRITICAL PERIOD FOR WEED COMPETATION IN SOYBEAN Glycine max (L.) Merr. UNDER IRAQI IRRIGATED AREAS

Abstract

Afield experiment was conducted during season 2012 to determine the Critical Period for Weed Competition in soybean crop growing under irrigated areas in Iraq to prevent unacceptable losses in yield. This period, expressed according to the growing periods of the soybean crop. The experiment included keeping plots free of weed at 1, 2, 3, 4, 5, 6, 7 and 8 weeks after emergence of soybean by removing weeds manually. Then, allowed weeds to grow after these periods until the end of the growing season. Results showed through the seasonal study that this period was during the fifth week after emergence depends on acceptable yield losses 3-5% in comparison of yield of free weed plots. Yield Losses of soybean resulting from weed competition along the growing season were 29.04%. Accordingly, this study recommends that weed control must continue until the fifth week after emergence and not to delay it for this period by using mechanical control methods or by using herbicides, which still effective against weeds until this period to avoid unacceptable loss of the economic yield and minimizing the negative impact of weeds environmentally and economically.