Abstract
The critical period for weed control (CPWC) is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. Field experiments were conducted in 2010 at the Oil Seeds Development and Cultural Company Experimental Station in the northern west of Iran to determine CPWC of soybean using a randomized complete block design with 8 treatments and three replications. The treatments were (1)weed-free and (2) weedy throughout a growing period of 20, 40, 60 and 80 days with regular weed-free, weedy checks. The CPWC was determined with the use of 5, 10 and 15% acceptable yield loss levels by non-linear regression method and fitting Logistic and Gompertz nonlinear equations to relative yield data. The CPWC of soybean was 10-40 day after emergence (DAE) to prevent yield losses of 10%. According to the results of the CPWC, growers could improve timing of post emergence herbicide applications and hand weeding.
