Insecticide Distribution Through an Irrigated Corn Canopy

Center pivot sprinkler systems can apply chemicals as well as water to crops. This study was conducted to determine the horizontal and vertical distribution of an insecticide applied with a center pivot irrigation system to a corn crop. The experiment was conducted at Tifton, Georgia, using a 140 m long, three-span center pivot system equipped with conventional impact sprinklers operating at 487-kPa pressure. An insecticide formulated with peanut oil was injected at a rate of 0.56 kg/ha with a calibrated metering pump into the irrigation mainline of the center pivot system with a gross irrigation application of 2.54 mm. Irrigation and chemical application uniformity were measured with glass collectors spaced 6.1 m apart along the lateral on bare soil. At three sites along the lateral at the midpoint of each span, the vertical chemical concentration was measured from above the canopy, at the third, sixth, and ninth leaf below the top of the corn plants. The mean irrigation application depth was 3.00 mm with a distribution uniformity of 93.5%. The mean chemical application amount was 0.79 kg/ha with a distribution uniformity of 83.9%. Chemical concentrations in relation to that in the water above the canopy declined 59, 49, and 39% at the third, sixth, and ninth leaf from the top of the plant with approximately 50% of the applied chemical retained on the corn foliage. The chemical distribution was less uniform than the water distribution and indicates the necessity of uniform irrigation applications to achieve high-chemical application uniformity.