Weed infestation is one of the main menaces of irrigated wheat production and productivity in Ethiopia. This experiment was conducted at Amibara and Fentale districts, to determine the appropriate period of herbicide application in irrigated wheat in Awash Valley. A total of ten treatments; 13, 18, 23, 28, 32, 38, 43 and 48 days after sowing along with a weed-free and weedy check were laid out in a Randomized Complete Block Design (RCBD) with three replication. The result revealed that weed

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... ity and biomass increased as weed competition periods increased, with the highest weed densities and biomass reported in weedy check in both study locations. The current study found that critical period of weed crop competition in wheat crop irrigated lowland areas were between 18 to 28 days after planting to avoid economic yield loss. Furthermore, weed growth was faster in the hot area and weed attained an economic threshold level earlier than in Ethiopia's highlands. Weed management in irrigated wheat conditions must be at the early seedling wheat crop stage. Future research should focus on evaluating various herbicides against broad leaf and grass weeds.