Effect of Weeding Time on the Species Composition, Plant Density, Dry Weight and Physiological Traits of Weeds in Corn (Zea mays L.)

In order to investigating the effect of weeding time on the species composition, plant density, dry weight and physiological characteristics of weeds in corn (Zea mays (L.) cv. SC 704), a field study was conducted at Sari Agricultural Science and Natural Resources University in 2006. The experiment consisted of 14 treatments which laid out in a randomized complete block design with 4 replications. The treatments included weed free and weed infested period to 4th leaf (V4), 6th leaf (V6), 8th leaf (V8), 10th leaf (V10), 14th leaf (V14), tasseling (T) and harvest stages (Full season weed infestation and weed control were the checks). Results showed that weeds density increased when weeds were allowed to grow until corn V8 stage and decreased after this stage, however, weeds could affect on corn plants because of increasing their dry weight and competitive ability. Results showed that weeds density and dry weight significantly decreased with increasing of weed control period length. Generally, velvetleaf (Abutilon theophrasti) with density around 50 percentage of total weed density during growing season has recognized as dominant weed and highest percentage of leaf index in weed infested period related to velvetleaf. Result indicated the peak competition period of weeds in corn crop was between V4 to V10 stages, thus if the weeds are controlled within this period, corn yield would be protected against a significant seed yield reduction.