Economic Analysis of Protectant and Disease-Forecast-Based Fungicide Spray Programs for Control of Apple Scab and Grape Black Rot in Ohio. R. C. Funt, Professor, Department of Horticulture, The Ohio State University, Columbus 43210. M. A. Ellis, and L. V. Madden. Professor and Associate Professor, respectively, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. Plant Dis. 74:638-642. Accepted for publication 19 December 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0638.

Fungicide trials were conducted from 1982 through 1988 at the Ohio Agricultural Research and Development Center, Wooster, to compare after-infection spray programs with protectant spray programs for control of apple scab and grape black rot. The timing of curative (after-infection) sprays was based on predicted infection periods determined by a commercially available microprocessor that monitors weather conditions and predicts infection. Except during 1984 on grapes, there were no significant differences between the after-infection and the protectant programs in disease control during all 7 yr of testing on both grape and apple. However, the after-infection program resulted in 26 and 34 fewer applications over 7 yr on apple and grape, respectively. An economic comparison of the two programs, based on the cost of fungicides, labor, and equipment, indicated a reduction in cost per unit of area with the after-infection program. The total cost reduction due to the after-infection program for grape during the 7-yr period in hypothetical 8.1-, 16.2-, and 32.4-ha (20-, 40-, and 80-acre) vineyards was estimated to be $16,234, $25,232, and $35,365, respectively, or $286, $222, and $156/ha ($116, $90, and $63/acre) annually. The total cost reduction over the same period for 8.1-, 16.2-, and 32.4-ha apple orchards was $4,385, $9,566, and $13,994, respectively, or $77, $84, and $62/ha ($31, $34, and $25/acre) annually. The curative fungicide program resulted in lower fungicide costs than the protectant program, but the savings were primarily due to reductions in labor and equipment costs.