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The Effect of Water Extracts of Spent Mushroom Compost on Apple Scab in the Field. D. S. Yohalem, Department of Plant Pathology, University of Wisconsin, Madison; E. V. Nordheim(2), and J. H. Andrews(3). (2)Departments of Forestry and Statistics, University of Wisconsin, Madison 53706; (3)Department of Plant Pathology, University of Wisconsin, Madison. Phytopathology 86:914-922. Accepted for publication 24 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-914.

To control apple scab disease caused by Venturia inaequalis, aqueous extracts from two sources of spent mushroom substrate (SMS), anaerobically fermented for 7 days and amended with spreader-sticker, were applied at weekly intervals to apple trees (cv. McIntosh) from green-tip to petal-fall and biweekly thereafter. Trials were conducted for three seasons at two locations in Wisconsin. Both extracts significantly reduced (? = 0.05) the leaf area affected by scab relative to water and spreader-sticker controls as evaluated by the Horsfall-Barratt scale. Disease incidence was similarly decreased but to a lesser extent. Extracts were not as effective in inhibiting disease as captan sprayed at the same intervals. No difference was detected between extracts with and without spreader-sticker. Higher populations of bacteria, which persisted for at least 1 month after the final spray, were detected on leaves treated with the extracts. No differences were found in total numbers of fungi. Inhibitory activity of extracts, assessed as in vitro inhibition of Venturia conidia germination, was monitored over time for extracts prepared from SMS stored under different conditions. For one source of SMS, neither time nor storage conditions (outdoors uncovered or indoors in sheds) affected inhibitory activity of extracts. Decline in efficacy of the other source was apparent by 13 weeks relative to unstored compost, although not between storage regimens.

Additional keywords: compost tea, filtrate, manure, Spilocaea, sustainable agriculture.