Comparison of Spray Droplet Size, Pesticide Deposition, and Drift with Ultralow-Volume, Low-Volume, and Dilute Pesticide Application on Apple. R. E. Barrat, Graduate Student, Department of Plant Pathology, West Virginia University, Morgantown 26506. J. L. Maas, Plant Pathologist, Fruit Laboratory, and H. J. Retzer, Agricultural Engineer, Agricultural Equipment Laboratory, ARS, USDA, Beltsville, MD 20705; and R. E. Adams, Plant Pathologist, Department of Plant Pathology, West Virginia University, Morgantown 26506. Plant Dis. 65:872-875. Accepted for publication 19 January 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1981. DOI: 10.1094/PD-65-872.

Fifteen-year-old trees of four apple cultivars were sprayed at rates of 9.4 L/ha (1 gal/A) for ultralow-volume (ULV) pesticide treatment, 190 L/ha (20 gal/A) for low-volume (LV) treatment, and 1,900 L/ha (200 gal/A) for dilute treatment. Thirteen sprays were applied, the first five following bud phenology and the rest as cover sprays. Fungicide deposits were monitored biologically with Penicillium variabile, and insecticide deposits were monitored analytically with high-pressure liquid chromatography. The ULV technique deposited at least as much pesticide on leaves as the other techniques, with less drift. Differences among arithmetic means at 2 and 4 m of the mass median and numerical mean diameters of spray droplets were 64.5 and 42.7 µm for ULV, 248 and 96.1 µm for LV, and 333 and 146.9 µm for dilute treatments. All treatments controlled Venturia inaequalis and Aphis pomi equally well at economically acceptable levels.