Assessment of Water Based Controlled Droplet Application of Insecticides on Lowland Rice

Abstract

Abstract An optimum droplet size for water based controlled droplet application (c.d.a.) on lowland rice was chosen by measuring the deposition rate for a 54 to 127 μm volume median diameter (vmd) range of droplet sizes on the canopy of the rice crop. The optimum size was 127 μm and this size was compared with knapsack spraying by measuring the deposition rate, at two growth stages, on the canopy and leaf sheath of the rice plant. The c.d.a. technique gave a predicted 30 to 40% reduction in applied dosage rate when spraying on the canopy, but no reduction was predicted for applications against the planthopper species which feed at the basal leaf sheath. The savings in labour and chemical for c.d.a. spraying were quantified in monetary terms, as well as the purchase price of the sprayers, using Philippine prices, c.d.a. gave a saving of US $8/ha over knapsack spraying and a locally manufactured sprayer could be made for US $25 cheaper than a knapsack sprayer.