|Grapevine Disease Notes|
DISEASE SUSCEPTIBILITY GUIDELINES
POWDERY MILDEW. Fruit: From pre-bloom to until 8 deg. Brix, usually about 3-4 weeks before physiological maturity. Shoots and foliage: From budbreak to killing frost. (Light PM on leaves late in the season may not be important on white cultivars but may need treatment on reds, where functional leaves are needed to ripen fruit adequately for wine-making.)
DOWNY MILDEW. Fruit: From pre-bloom through harvest, though the likelihood of infection is highest (1) when the fruit are pea-sized and (2) in the fall before harvest, when nights become cooler. Shoots and foliage: From 5-6 leaves (10 to 12-inch shoot length), if the pathogen is active that early, to killing frost.
BLACK ROT. Fruit: From pre-bloom until 3-4 weeks after bloom for native grapes and up to 6 weeks for vinifera varieties, when fruit become immune. Shoots and foliage: Young, green shoots and emerging leaves are susceptible at any time of the season, but most infections occur between budbreak and the end of bloom.
PHOMOPSIS. Fruit: Most infections occur from pre-bloom to 4 or so weeks after bloom. Shoots and foliage: Most infections occur between budbreak and pre-bloom.
BOTRYTIS. Fruit: Most infections occur between bloom (immediate pre-bloom in wet weather) and post-bloom. Other critical periods for infection, especially on tight-clustered varieties, are bunch closing (berry touch), veraison, and pre-harvest, especially in wet weather.
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