Effects of Fungicides that Inhibit Ergosterol Biosynthesis on Apple Powdery Mildew Control, Yield, and Fruit Growth Factors. R. A. Spotts, Associate Professor, Oregon State University, Mid-Columbia Experiment Station, Hood River 97031. L. A. Cervantes, Experimental Biology Technician, Oregon State University, Mid-Columbia Experiment Station, Hood River 97031. Plant Dis. 70:305-306. Accepted for publication 14 October 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-305.

The effects of triadimefon, etaconazole, and dinocap on apple powdery mildew control, fruit set, size, shape, percent floral buds, and yield were studied on mature cultivar Newtown apple trees on seedling rootstock in four successive years. Treatments were applied to the same 0.2-ha blocks each year at 561 L/ha at 1-cm green, pink, petal fall, and first cover. Triadimefon, etaconazole, and dinocap rates were 0.14, 0.10, and 0.55 kg a.i./ha, respectively. Triadimefon and etaconazole reduced leaf and bud mildew infection more than either dinocap or check treatments. None of the mildewcides affected percent floral buds or fruit set, size, or shape. Yields of trees treated with etaconazole and dinocap were not different from each other but were greater than yield of triadimefon or check trees.