A comparison of motorised knapsack mistblower, medium volume application, and spinning disk, very low volume application, of Helicoverpa armigera nuclear polyhedrosis virus on cotton in Thailand

A wettable powder formulation of Helicoverpa armigera nuclear polyhedrosis virus (NPV) was applied against larvae of the cotton bollworm (Helicoverpa armigera) (Hubner) in Thailand. Field trials were carried out on rainfed co tton in September and October 1995 to investigate the efficacy of spinning disk spray application, at very low volume (VLV) rates, compared to motoris ed knapsack mistblower spray application at medium volume (MV) rates. Trial s were done to ascertain if any control benefits would arise from using VLV spinning disk sprayers as an alternative application method to mistblower sprayers (at medium volume) commonly used on cotton in Thailand. Sprayer pe rformance was assessed by bioassay of leaves sampled from spinning disk VLV and mistblower MV spray application plots. Volumes of spray deposited were determined and measurements of droplets deposited on targets attached to l eaves were made. The results of leaf sample bioassays indicated that VLV ap plication by a spinning disk sprayer gave better control than did MV applic ation by a mistblower. (C) 1999 Elsevier Science Ltd. All rights reserved.