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Development and Evaluation of an Integrated, Reduced-Spray Program Using Sterol Demethylation Inhibitor Fungicides for Control of Primary Apple Scab. W. F. Wilcox, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. D. I. Wasson, and J. Kovach. Cornell Cooperative Extension, Lake Ontario Fruit Program, P.O. Box 150, Albion, NY 14411; and Integrated Pest Management Program, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. Plant Dis. 76:669-677. Accepted for publication 30 January 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0669.

An integrated, reduced-spray program for control of primary apple scab infections was developed and evaluated for three consecutive years in nine commercial apple orchards and for 2 of the same 3 yr in five additional orchards in western New York. Growers were advised to make four applications of a sterol demethylation inhibitor fungicide (i.e., fenarimol, flusilazol, or myclobutanil), whose timings were to be independent of the occurrence of apple scab infection periods but were to coincide with applications of insecticides or acaricides at or near the following four phenological stages: 1) tight cluster; 2) pink bud; 3) petal fall; and 4) approximately 10 days after petal fall (first cover spray). This schedule contrasts with a traditional primary scab control program averaging six or seven fungicide applications commencing shortly after budbreak and timed according to anticipated or recent weather events. The mean incidence of apple scab on fruit at harvest in all orchards was 0.2, 1.0, and 1.6% in 1988, 1989, and 1990, respectively, during which an average of 5.2, 14.4, and 8.2 primary scab infection periods occurred in these locations; however, when data from one orchard were not considered, mean fruit scab incidence was only 0.4 and 0.5% in 1989 and 1990, respectively. Including early-season copper sprays applied in some orchards for control of fire blight, the mean number (and range) of fungicide sprays actually applied in the trial orchards during the period of primary scab development was 4.1 (35), 4.4 (45), and 4.5 (36) in 1988, 1989, and 1990, respectively; within these ranges there was no apparent relationship between the number of sprays applied and the degree of control obtained. This program has reduced fungicide use and pesticide application events simply and effectively, although its limitations are acknowledged and discussed.

Keyword(s): integrated pest management, Venturia inaequalis.