Critical Period of Weed Control of Corn (Zea mays L.) Second Cropping at Moghan Region

Moghan region, North West of Iran, is one of the important producers of the corn in the country. To determine the critical period of weed control in corn as second crop in this region, an experiment was carried out in a randomized complete blocks design with four replications during 2010 in the Parsabad Moghan climatic conditions. Two methods of weed control treatments were used. In the first method, weeds controlled at 0, 10, 20, 30, 40, 50 and 60 days after corn emergence. (DAE), and then weeds were allowed to grow until harvest and in the second method of weed control, weeds were allowed to grow during 0, 10, 20, 30, 40, 50 and 60 DAE, and then the plots were kept free of weeds until harvest. The regression was used to determine the relationship between yield and different control periods and weed interference. The results showed that periods of weed- free and weed- infested plot affected differently the dry weight and number of weeds in all treatments. Generally the results showed that critical period of weeds control in corn (AYL) based on growing degree days (GDD) after sowing considering 5% acceptable yield loss, it is necessary to control weeds in a period between 1-67 days after planting or 90-1051 growing degree days and period of weeds control in corn (AYL) based on growing degree days (GDD) after sowing by considering 10% acceptable yield loss, weed control is necessary between 3-52 days after planting or 132- 844 growing degree day.