عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Field experiments were conducted to investigate the effect of herbicide doses on corn-multiple weed competition. Sixteen weed density combinations consisting of 4 densities of redroot pigweed × 4 densities of common cocklebur under five doses of herbicide were assessed. The two weed species responded differently to herbicide doses. Competitivity of redroot pigweed decreased with increasing herbicide dose and was completely removed by applying herbicide at 0.5 of full recommended dose, but for common cocklebur an initial increase occurred at 0.25 rate of full dosage. The relationship between weed competitivity and herbicide dose was well-described by standard dose response curve and Brain & Cousens model for redroot pigweed and common cocklebur, respectively. A combined model incorporated standard dose response curve and Brain & Cousens function into the multivariate rectangular hyperbola competition model gave a good description of corn yield. When no herbicide was applied, the competitivity of common cocklebur was approximately 1.7 times greater than that of redroot pigweed and 63% of yield loss occurred from the combination of 8 common cocklebur and 12 redroot pigweed plants m-2. Where the density of common cocklebur was low (0 to 4 plants m-2) applying herbicide at half the full recommended dose could save the yield, but with increase in common cocklebur density, the herbicide reduced doses failed to prevent the yield loss. Even at full recommended dose of herbicide, corn yield suffered loss of 6 to 10 percent from high density of common cocklebur. Nomenclature: Nicosulfuron; common cocklebur, Xanthium strumarium L.; redroot pigweed, Amaranthus retroflexus L.; corn, Zea mays L.