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Disease Control and Pest Management

Suppression of Cedar Apple Rust Pycnia on Apple Leaves Following Postinfection Applications of Fenarimol and Triforine. R. C. Pearson, Assistant professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Geneva, NY 14456; M. Szkolnik(2), and F. W. Meyer(3). (2)(3)Professor, and research technician III, respectively, Department of Plant Pathology, New York State Agricultural Experiment Station, Geneva, NY 14456. Phytopathology 68:1805-1809. Accepted for publication 8 July 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1805.

The experimental fungicides fenarimol and triforine were compared with mancozeb to determine control of cedar apple rust (caused by Gynmosporangium juniperi-virginianae) following postinfection applications to apple under both greenhouse and orchard conditions. Fenarimol and triforine inhibited normal development of pycnia and only small flecks developed. In the greenhouse, fenarimol at 20, 40, and 60 μg/ml provided 98% control when applied 3 days after inoculation; triforine at 120, 240, and 360 μg/ml provided 8998% control 1 day after inoculation with 5994% and 6883% control after 2 and 3 days, respectively. In the orchard, fenarimol at 20 and 40 μg/ml suppressed pycnial formation 9699% and 97100%, respectively, when applied 5 or 7 days after commencement of infection periods. Triforine at 240 μg/ml suppressed pycnial formation by 8083% with sprays within 2 days after infection in the orchard, but control decreased to 71 and 79% at 3 or 5 days. Inadequate control was obtained with postinfection applications of mancozeb, a commonly used rust fungicide, in either greenhouse or orchard.

Additional keywords: Malus pumila.