Evaluation of the Tree-Row-Volume Model for Full-Season Pesticide Application on Apples. T. B. Sutton, Department of Plant Pathology, North Carolina State University, Raleigh 27695. C. R. Unrath, Department of Horticultural Science, North Carolina State University, Raleigh 27695. Plant Dis. 72:629-632. Accepted for publication 9 February 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0629.

Chelated micronutrients were used to monitor spray deposits in apple trees resulting from dilute applications with an airblast sprayer at tight cluster, first cover, or fifth cover. Rates per hectare were adjusted before each application, according to a tree-row-volume model (TRV). Applications at phenophase tight cluster resulted in mean deposits 1.2–2.0 times greater than applications made at first or fifth cover. Increased deposit at tight cluster generally was consistent among trees pruned at three management levels (light, moderate, and heavy) and in two orchards with different size trees. Variation in deposit within trees was greater in larger trees in the Hillcrest Orchard than in smaller trees in the Justice orchard. The greater variation at Hillcrest was probably related to the difficulty of propelling water droplets throughout the canopy of large trees (up to 6.53 m tall and 8.69 m wide). Our results indicate that the TRV model is a suitable guide for early season as well as cover spray applications. The increased deposit obtained at tight cluster should not be viewed as justification for reducing pesticide rates per hectare in early season sprays.