Application Rates and Spray Intervals for Apple Scab Control with Flusilazol and Pyrifenox. A. L. O'Leary, Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824. A. L. Jones, and G. R. Ehret. Department of Botany and Plant Pathology and the Pesticide Research Center, Michigan State University, East Lansing 48824. Plant Dis. 71:623-626. Accepted for publication 19 February 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0623.

The triazole fungicide flusilazol and the pyridine fungicide pyrifenox, both ergosterol biosynthesis inhibitors, effectively controlled apple scab under greenhouse and orchard conditions. In greenhouse studies, single sprays of flusilazol at 8 µg/ml and pyrifenox at 38.4 µg/ml inhibited the development of visible scab lesions on apple leaves when applied 72 hr after inoculation. When sprays were applied 120 hr after inoculation, chlorotic rather than normal lesions formed. No normal lesions and fewer chlorotic lesions developed when two sprays were applied 7 days apart beginning 72 and 120 hr after inoculation. Single sprays of flusilazol or pyrifenox applied 24–72 hr before inoculation gave control of leaf scab comparable to that provided by 1,200 µg/ml captan applied at the same interval. When the interval was extended to 120 hr, captan was more effective. In field studies over a 3-yr period, flusilazol at 9.4–14 µg/ml and pyrifenox at 37.5–75 µg/ml were both highly effective in 7-day schedules for control of apple scab. Lower rates and 14-day schedules were less effective. Flusilazol at 37.5 µg/ml on a 21-day schedule was highly effective for suppressing lesions. Mixtures of flusilazol at 9 µg/ml with mancozeb at 1,440 µg/ml and of pyrifenox at 37.5 µg/ml with metiram at 1,900 µg/ml were more effective than either flusilazol or pyrifenox alone on 14-day schedules.

Keyword(s): Venturia inaequalis.