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Grape (Vitis spp.) - Powdery Mildew
Notes Erysiphe necator (formerly Uncinula necator), a fungal disease common to all areas of the Pacific Northwest. Hosts include grape, Boston ivy, Virginia creeper, and Ampelopsis (porcelain berry). More likely to be found west of the Cascades. Most of the biology is known from research on grapes. The fungus may overwinter as a group of thin threads called hyphae, inside the vine's dormant buds and/or as small black bodies (chasmothecia) on the exfoliating bark of the vine. Many asexual spores (conidia) are produced on the surface of powdery mildew colonies. Whitish or grayish patches form on leaves and, if severe, ultimately cover both surfaces. Tactics that increase sunlight exposure to leaves reduce powdery mildew severity. Chemicals used for leaf spot will be helpful to manage powdery mildew.