The critical period of weed control in corn (Zea mays L.) in sari condition

In order to study the effect of competition of weeds on corn yield and yield components of corn، an experiment was conducted at Research Station of Sari Agricultural Sciences and Natural Resources University in 2006. The experiment consisted of 14 treatments which lay out in a randomized complete block design with 4 replications. The treatment included weed free and weed infested period to 4th leaf (V4)، 6th leaf (V6)، 8thleaf (V8)، 10th leaf (V10)، 14th leaf (V14)، tasseling (T) and Harvest stage (full season weed infestation and weed control were the checks). According to results، weeds dry matter increased with increasing of the weedy period length. Continuation of weed competition to the later stages of crop development caused significant decreasing of ear length، rows per ear and kernel per rows and grain yield. Generally، the peak competition period of weeds in corn crop was between 4leaf stages to 10 leaf stage، thus if the weeds are controlled within this period، corn yield would be protected against a significant seed yield reduction.