Deposition Efficiency from Aerial Application of Postemergence Herbicides

Abstract

This study was designed to determine the effect of application parameters on spray deposition from aerial application of a mixture of tridiphane, atrazine, and crop oil concentrate. Variables evaluated included nozzle orientation (0 and 90 deg), spray application rate (18.7 and 46.8 L/ha), and airspeed (144 and 208 km/h). Spray deposit was measured from mylar plates, polyethylene soda straws, water-sensitive cards, water-sensitive straws, and yellow foxtail (Setaria glauca) plants. Biological response (% control of yellow foxtail) from each application was rated at 1 and 2 weeks following application. The collectors were placed between the center lines of two adjacent spray swaths flown directly into the wind. Two sample lines, 15-m apart, were placed perpendicular to the direction of flight. The first line consisted of 17 mylar plates, 5 flats of plants, 5 straw stands (each containing 10 soda straws and one water-sensitive straw) and 5 water-sensitive cards. The second line consisted of 17 mylar plates and 5 flats of plants. The collectors were gathered at the end of each treatment and transported to the laboratory for processing and analysis. Treatments were replicated three times. Wind speed and direction, temperature, and relative humidity were recorded during each test. Data from the mylar plates indicated that percent deposit of fluorescent dye at 46.8 L/ha spray mixture application rate was significantly higher than for the 18.7 L/ha rate. The percent deposit for the 144 km/h airspeed and the 46.8 L/ha application rate was higher than for the 208 km/h airspeed and the 18.7 L/ha application rate. There was no difference in deposit due to nozzle orientation. Deposits on the plant leaves indicated differences due to application rate, airspeed, and nozzle orientation. The highest deposit on plant leaves was obtained with the 46.8 L/ha application rate, 90 deg nozzle orientation and 208 km/h airspeed. The correlation coefficient for deposits on plants and straw collectors was 0.58. For deposits on plants and mylar plates the correlation coefficient was 0.54.