You can apply at the rate of 1 cup Epsom salts to 1 gallon water, sprayed on leaves. Rock Dust is an excellent source of this mineral. Potassium A great stress reliever for plants. Increase absorption of calcium and magnesium. A natural fungicide.
Sulfur Is an ancient tool of the organic farmer.
A natural fungicide and insecticide. Used for rust, powdery mildew, leaf spot, brown rot. Also a good soil acidifier. Micronized sulfur is an extremely fine dust which when dusted on plants will control apple scab, cedar-apple rust, black rot, leaf spot, and powdery mildew. Liquid sulfur is also available.