Field Performance of Sterol-Inhibiting Fungicides Against Apple Powdery Mildew in the Mid-Atlantic Apple Growing Region. K. D. Hickey, Professor of Plant Pathology, Department of Plant Pathology, Pennsylvania State University Fruit Research Laboratory, Biglerville 17307. K. S. Yoder, Assistant Professor of Plant Pathology, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University Fruit Research Laboratory, Winchester 22601. Plant Dis. 65:1002-1006. Accepted for publication 5 March 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-1002.

Eight sterol-inhibiting fungicides evaluated in 18 orchard spray trials were highly effective against apple powdery mildew. All were significantly more effective than standard fungicides. Because of their broad spectrum of disease control, they appeared promising as new orchard fungicides. Mildew incidence on terminal leaves of Rome Beauty apple ranged from 0 to 23% when treated seasonally under moderate to severe disease conditions. The amount of active ingredient required to provide commercial control (less than 20% incidence) varied among the fungicides. Subgroups based on the range of active ingredient needed were CGA 64251 and fenarimol at 10–20 mg/L, triarimol and triadimefon at 25–75 mg/L, bitertanol and triforine at 75–120 mg/L, and prochloraz and fenapanil at 180–300 mg/L.