In apple farming, the use of sulfur spray has been used for many years as an organic alternative to poisonous fungicides. The use of sulfur can cut down and kill fungal infections on trees.
Sulfur comes in a few different varieties, such as liquid lime sulfur, dry wettable powders and formulations that are liquid. Mixing of sulfur for use should be done according to the instructions on the label. Some local laws may prohibit the use of certain materials, so learn the guidelines before using sulfur sprays.
Sulfur is highly effective against powdery mildew attacks on plants and can be used against apple scab.
Sulfur, although effective, does not have any residual power, meaning the sulfur spray will only be active for a short time after application. Sulfur spray needs to be applied every three to five days to remain effective. If using sulfur spray alone, up to 25 applications may be needed during the regular growing season, according to Ohio State University. Lime sulfur should not be applied until three weeks after any oil spray on the apple tree; the two are incompatible.
If using sulfur as a spray for organic farming, the spraying schedule will largely rely upon the weather conditions. Sulfur should be applied just before rains during infection periods (such as from green tip of the apple tree until there is a 1/2 inch of green tip). Spraying should be done again every three to five days unless more rain is forecast.
Although it's an organic material, safety precautions do need to be heeded for spraying sulfur on apple trees. Respiratory protection, such as a mask that cleans the air up to 10 times the Permissible Exposure Limit and the Threshold Limit Values (PEL/TLV) of local guidelines, should be worn at all times. Protective eyewear and long clothing should be worn as well.