Interaction and Control of Alternaria Stem Decay and Blue Mold in d'Anjou Pears. J. W. Sitton, Technician, USDA, ARS, Department of Plant Pathology, Washington State University, Pullman 99164. C. F. Pierson, Research Plant Pathologist, USDA, ARS, Tree Fruit Research Center, Wenatchee, WA 98801. Plant Dis. 67:904-907. Accepted for publication 28 January 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/PD-67-904.

Decay of stems of d'Anjou pears by Alternaria alternata is found in fruit treated with benomyl postharvest drench for control of Penicillium expansum and subsequently held in storage for prolonged periods. Benomyl favors the incidence of A. alternata, a slower growing and less competitive fungus than P. expansum, at the osmotic potential (–22 bars) and temperature (near 0 C) conditions of pears in storage. Prochloraz, chlorothalonil, iprodine, and triadimenol, in combination with benomyl, were effective in controlling Alternaria stem decay and blue mold on fruit treated and stored for 6 or 7 mo in cold storage. The most effective control of both Alternaria stem decay and blue mold was obtained with 1,000 μg/ml prochloraz combined with 500 μg/ml benomyl. Reduction of linear growth of A. alternata on potato-dextrose agar amended with prochloraz was not a useful method for determining the most effective concentration for disease control; 1 μg/ml inhibited mycelial growth of Alternaria but 1,000 μg/ml was required for disease control.