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.
Sulfur is also available in rock dust, gypsum. Zinc is normally readily available but when the flow of the over 72 minerals needed by the soil and plants is interrupted, the zinc will be used up by the plants. When the plants don't have any zinc left they go into immediate stress.