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  • Author or Editor: Colleen Harlton x
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There is very little information on the interaction of wine grape microflora with fungicides used to control grape diseases. The objective of this study was to determine how fungicides used in a standard grape pest management program and an experimental clay being developed for control of powdery mildew affect grape microflora. Grape leaves and fruit were surveyed for bacteria, fungi and yeast six times over the growing season in 2000 after treatment with clay or fungicides. In 2001 only clay was studied for control of powdery mildew in `Chancellor' grapes. The total number of propagules present on untreated leaf and fruit tissue were 76% bacteria, 14% yeast, and 9% fungi. Fungicides used for grape disease control significantly reduced epiphytic fungi (P < 0.0001), bacteria (P = 0.03), and yeast (P = 0.0001) on grape berries and epiphytic fungi (P < 0.0001), and yeast (P = 0.03) on leaves. The clay treatment had no detectable effect on grape microflora because no significant differences were recorded between clay or untreated grape berries or leaves on any of the sampling dates. Over the growing season the fungicide spray program reduced incidence and severity of powdery mildew better than clay. Clay controlled powdery mildew on `Chancellor' fruit in 2000 and 2001.

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