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Environmental Effects on the Development and Dissemination of Cladosporium carpophilum on Peach. Ernest G. Lawrence, Jr., Former graduate assistant, Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29631, Current address of senior author: Stauffer Chemical Co., 5137 Revere Rd. #36, Durham, NC 27713; Eldon I. Zehr, professor, Department of Plant Pathology and Physiology, Clemson University, Clemson, SC 29631. Phytopathology 72:773-776. Accepted for publication 21 October 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-773.

In the laboratory, mycelial growth of Cladosporium carpophilum was best at 2030 C, and conidial germination was best at 98100% relative humidity (RH). Some conidia germinated on glass coverslips without free water, but conidia germinated much more readily on water agar. Sporulation on twig lesions occurred at 80100% RH, but was most abundant at 98100%. Some peach scab lesions appeared on new twig growth about the same time as on fruit and they became numerous on twigs later in the season. The fungus did not sporulate abundantly in lesions until after overwintering. At 100% RH. C. carpophilum produced conidia in lesions for 2030 hr, after which conidia were released. Moistening infected twigs before exposure to 100% RH did not increase production of conidia. Conidia were present in the atmosphere of a peach orchard and in rainwater runoff from infected twigs. In the spring, conidia were most abundant 26 wk after the calyx-split stage of development. High numbers of conidia were not always associated with rainfall. Conidia of C. carpophilum were most numerous early in May.

Additional keywords: spore sampling.