Modeling Annual Weeds Seedling Emergence in Common Bean (Phaseolus vulgaris L.) Along with Weed Management

Models that simulate weed seedling emergence as functions of thermal time would help minimize herbicide use by the optimization of the timing of weed control. The objective of this research was to introduce a model to predict barnyardgrass [Echinochloa crus-galli (L.) P. Beauv]، redroot pigweed (Amaranthus retroflexus L.) and common lamb''s-quarters (Chenopodium album L.) seedling emergence in the presence of common bean canopy. Weed seedling emergence data in 2010 (spring and summer) were used to model the pattern of each species as a function of the thermal time in the 5 cm upper layer of the soil profile. Two functions: Weibull and Gompertz were used to describe the relationship between thermal time and weed seedling emergence. The Gompertz function closely predicted (RMSE= 5. 3–6. 7%) the relationship between thermal time and seedling emergence for all three species. Conversely، Weibull function except for redroot pigweed gave worse fit. The three species also showed different patterns of emergence and thermal time required for the onset of emergence and species can be grouped into two emergence time-span groups. In the fist group، redroot pigweed and barnyardgrass had a shorter emergence time-span requiring 391-488 thermal time for full emergence. In the second group، common lamb''s-quarters had a long-lasting emergence، requiring 620 thermal time to complete this process. Difference in emergence pattern of these weed suggest that barnyardgrass and redroot pigweed should be given a higher priority for control than common lamb''s-quarters in common bean.