Use of Water-Sensitive Paper to Monitor the Deposition of Aerially Applied Insecticides

Water-sensitive papers (WSP) were placed on top of 20-cm stakes above the crop canopy to monitor the deposition of aerially applied deltamethrin and permethrin. A residue analysis method with 97% mean recovery was developed to determine amounts of insecticide on the WSP. Over four applications, the mean deposition on the WSP was 59-75% of applied insecticide. The WSP had 91% trapping efficiency for the spray droplets and gave excellent images for visual assessment of the spray deposits. Droplets per square centimeter were a good indicator of the relative amount of insecticide deposited between two formulation treatments. Comparing droplets per square centimeter on horizontal WSP with vertical WSP gave an estimate of the mean angle of incidence of the spray droplets. Droplet size spectra were obtained from manual measurement of the WSP images, but such size determinations were subject to several sources of error. The use of WSP to monitor spray deposition in aerially applied insecticide trials is recommended.