There are differences in the dynamical nature and behavior of powdery mildew on different hosts. Growers and consultants tend to have their own treatment methods, different approaches, fungicides preferences, and secret tricks. Still, some consensus does exist: prevention, rotation, and the use of several fungicides that each belong to a different group (with respect to mode-of-action).
Effective control requires spraying with high pressure, high volume of water; good coverage is of the essence. Having a fixed or dynamic schedule for spraying application is a common strategy.
The following is a list of generic names of fungicides used in one or more parts of the world and is sorted into groups according to their mode of action:
Group 1: Penconazole, triadimenol, rebuconazole, myclobutanil, tetraconazole, propiconazole, prochloraz, cyproconazole , difenoconazole, fenbuconazole, and triflumizole
Group 2: Azoxystrobin, pyraclostrobin, trifloxystrobin, and kresoxim-methyl
Group 3: Sulfur, copper sulfate, bicarbonates, mineral oils, neem oil, and detergents\soap-based products
Group 4: Proquinazid
Group 5: Fluopicolide
Group 6: Metrafenone
Group 7: Cyflufenamid
Group 8: Quinoxyfen
Group 9: Fluopryam
Group 10: Polyoxin
Sulfur can cause injury to foliage and fruit when applied on days with a temperature above 32 C. Do not apply within 2 weeks of an oil application.
When powdery mildew is present yet the symptoms have not appeared, consider spraying applications of fungicides once every 7-14 days. Don’t use products based on the same active ingredient in consecutive treatments except in group 3, as there are no restrictions there.
Use fungicides belonging to different groups to prevent pathogens from developing resistance to a specific chemical.
Some commercial fungicides that have two active ingredients and two modes of action. After using such products, take into account that now you have two groups that you already used. So, make sure to exclude those two active ingredients in the next application.
It is important to remember that if powdery mildew develops resistance to fungicides within a group, the pathogens are likely to be resistant to all members of that group (except group 3).
In most cases, if powdery mildew is not visible when fruit begins to change color then a new infection will not occur, and there is no need for more applications of fungicides.