Evaluation of insecticide residues and droplet drift following aerial application to cotton in New South Wales.

Abstract

In a study to determine the extent of off target drift from aerial spraying, insecticides were applied to cotton crops in various strengths of crosswind by an aircraft fitted with rotary atomizers. Both water-based and oil-based sprays were applied, at 20 and 2 litres/ha respectively. Compared with the mean insecticide deposit across a 16-m target swath, in seven runs, the mean recoveries of insecticide 15, 165 and 3 15 m downwind from the edge of the swath were 6.8, 0.13 and 0.002% respectively. Deposition on plants was nearly twice that on the ground, but the proportional decline downwind was similar. Counts of droplets deposited on paper targets fixed to masts showed that the dispersing cloud of water-based spray contracted more rapidly than did that of the oil-based spray, probably because of greater evaporation of the former. The results indicate that a 300-m wide buffer zone between target crops and areas susceptible to contamination should be adequate under most conditions.