According to “The Pacific Northwest Plant Disease Management Handbook,” grape powdery mildew represents “A fungal disease common to all areas of the Pacific … By: Becky Garrison. Grape (Vitis spp. On the fruit, the fungus at first may appear grayish or whitish, but later is has a brownish russeted appearance. Grapevine powdery mildew is one such disease, and is present in almost all international viticulture areas where susceptible grape varieties are produced. Symptoms. Side-by-side comparison of downy and powdery mildew on grape leaf. Symptoms will vary depending on the age of leaf tissue. Grape powdery mildew (Erisiphe necator, syn. Jay W. Pscheidt, 2017. Powdery mildew is a fungal disease that can affect a variety of plants. Grape Powdery Mildew December, 2015 Grape powdery mildew is caused by the fungus Uncinula necator. )-Powdery Mildew. SyMPtoMS Powdery mildew… Interior. This fungus has a narrow host range attacking only grape plants and a few related species. This disease is predominately driven by weather and … It is the most common and widespread disease of grapevines in the B.C. Uncinula necator) is the most significant disease in terms of expenses for control and losses in quality and yield faced by grape growers in California, as well as worldwide. Grape Powdery Mildew Guide H-329 Bernd Maier and Natalie Goldberg1 Cooperative Extension Service • College of Agricultural, Consumer and Environmental Sciences This publication is scheduled to be updated and reissued 6/15. New leaves infected by downy mildew often … Powdery mildew is best seen on … Popular wine grape varieties vary in susceptibility to powdery mildew… Powdery mildew is a common disease that imposes large economic costs on California grape growers.