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Ecology and Epidemiology

Seasonal Incidence of Fungi in Symptomless Cranberry Leaves and Fruit Treated with Fungicides During Bloom. Steven N. Jeffers, Department of Plant Pathology, University of Wisconsin, Madison 53706; Phytopathology 81:636-644. Accepted for publication 29 January 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-636.

In 1987 and 1988, leaves and fruit were collected at 2-wk intervals for 20 wk from replicated plots at two commercial cranberry (cultivar Searles) marshes in central Wisconsin. Leaves were collected from budbreak, and berries were collected from 8 and 6 wk after budbreak in 1987 and 1988, respectively, until harvest. Beginning during bloom, captafol, chlorothalonil, and mancozeb were applied to plots three times at 14-day intervals to manage postharvest storage rots. Control plots received no fungicide. Fungi were isolated from surface-disinfested, symptomless leaves and berries on all sampling dates in both years. In all, 33 genera or species of fungi were identified. Of these, only seven were known pathogens (Apostrasseria lunata, Botryosphaeria vaccinii, Glomerella cingulata, Godronia cassandrae, two morphologically distinct types of Physalospora vaccinii, Phytophthora sp., and Pyrenobotrys compacta), and three were possible pathogens. B. vaccinii and P. vaccinii were recovered most frequently and consistently. The proportion of leaves or berries from which fungi were isolated (i.e., incidence) increased as the season progressed. Although there was no significant difference among fungicide treatments in seasonal incidences of fungi from either leaves or berries, fungicides delayed the time, by 26 wk, at which incidences began to increase in both leaves and berries compared with untreated controls. By the end of the season, fungicides had reduced the number of fungus colonies and the incidence of B. vaccinii from berries in both years and the number of fungus colonies from leaves in 1987; however, final incidences of P. vaccinii (either type), Alternaria, and miscellaneous other fungi were not affected. Incidences of most fungi began increasing in both treated and untreated leaves and berries at 1012 wk after budbreak, after the last fungicide application had been made, and continued to increase up to harvest. Initiating fungicide applications after bloom, at approximately 10 wk after budbreak, should reduce the incidence of fungi in cranberry leaves and berries more effectively than earlier applications.

Additional keywords: endophytes, Vaccinium macrocarpon.