Had slight mildew last year and sprayed with bordeax mix in spring.
Many organic fungicides work best using a schedule of spraying every 7 to 10 days, from early spring, till your grape berries enter veraison (i.e. maturity often easiest seen as color change in red grapes).
Yes, you can spray less with organic sprays. As some years, that may be very hot and dry, will need less spraying. But another year that is just a little bit more cool and moist can result in lost crops if not sprayed enough. To know how to optimally spray is complicated, and to get best results, spaying on a simple schedule is most effective.
Also strange white an pink long growths from trunk about 4 ft up.
View attachment 76700
I suspect those are simply areal roots.
Aerial roots on a grapevine in eastern Minnesota. Photo: Annie Klodd Author: Annie Klodd, Extension Educator - Fruit and Vegetable Pro...
blog-fruit-vegetable-ipm.extension.umn.edu
If those appear, you probably have a lot of humidity this year, which is why your grapes are also showing fungus due to not spraying enough, or your vines may be stressed (too much heat, water stress, disease stress, etc.).
Hope this helps.
