This product is especially useful for garden use. However, sulfur can be damaging to some squash and melon varieties. Timing for sulfur treatment in apples and grapes is described below. Fungicides can also be used on other tree fruits and vegetables but should rarely be needed for powdery mildew control. Sprays are not necessary in many backyard situations.
Powdery mildew is a perennial problem in grapes.
Begin applying sulfur when all buds have pushed. Thereafter, repeat at 10-day intervals until the sugar content of grapes is 12 to 15 percent, which is when they begin to soften and approach ripeness and are no longer susceptible to infection. You can measure the sugar content with a refractometer, if you have access to one, or you can see if sample berries sink in a 15 percent sucrose solution. A Grower's Guide to Using Less Pesticide, Univ. Resources Publication 3332, Oakland.