Determination of critical period of weed control in corn (Zea mays L.) in Ahvaz region

In order to determine the critical period of weed control in grain corn (Zea mays L.), a field study was conducted at the Ramin University ofAhvaz Research Field in 2009. The experiment was designed according to randomized complete block design. Treatments consisted of two different periods of weed interference, a weed-free period and a weed removal period, imposed at V2, V5, V8, V11, Tassel, and harvest (based on phonological stages of corn development). The relationships between grain yield and different weedy or weed-free periods were determined via regression analyses. Cyperus sp., Echinochloa crus-galli, Convolvulus arvensis and malva sp. were naturally infested on experimental plots. Results suggested that a weed-free period between 2-11 leaf stages of maize (GDD= 500-1125) was enough to provide acceptable grain yield. Based on weed infested treatments, a weed free period until theV8 stage was enough to reduce weeds number and dry weight to 64 and 84/6% respectly. Weed interference until late in the season reduces grain yield, biologic yield and harvest index of corn to 36, 28/6 and 19/6% respectly. Thus, it is possible to optimize the timing of weed control, which can serve to reduce the costs and side effects of intensive weed control.