Ultralow-Volume Spray Control of Three Apple Diseases. H. L. Keil, Plant Pathologist, Fruit Laboratory, Agricultural Equipment Laboratory, AR-SEA, USDA, Beltsville, MD 20705. H. J. Retzer, Agricultural Engineer, Agricultural Equipment Laboratory, AR-SEA, USDA, Beltsville, MD 20705; R. E. Barrat, Graduate Student, Department of Plant Pathology, West Virginia University, Morgantown 26506; and J. L. Maas, Plant Pathologist, Fruit Laboratory, AR-SEA, USDA, Beltsville, MD 20705. Plant Dis. 64:681-684. 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, 1980. DOI: 10.1094/PD-64-681.

Ultralow-volume (ULV) application of fungicides satisfactorily controlled Venturia inequalis, Podosphaera leucotricha, and Gymnosporangium juniperi-virginianae. Fungicides were applied with a modified Kinkelder model 3P-50 Pony sprayer at ultralow-volumes on four varieties of full-size apple trees in a seasonal program. Droplet size emitted by the Kinkelder averaged 20 µm. Rates averaged 14 L/ha. No clogging occurred when vacuum jet atomizers were used with combinations of wettable powder and emulsifiable fungicides. A leaf disk bioassay was performed with Penicillium variabile as the detector organism to monitor levels of initial and residual benomyl deposits on apple foliage. Concentrations of benomyl were highest on lower leaf surfaces closest to the sprayer and lowest in the tree interior. An average 50% activity of benomyl was lost 1 wk after application to foliage.