Whether you're growing a few apple trees or an entire orchard full, a fungicide program will be necessary. For organic gardeners, control of powdery mildew, apple scab and cedar-apple rust may involve using sulphur spray.
Sulphur as a Fungicide
Sulphur has been used as an organic fungicide for centuries, and is sprayed on crops like apples, stone fruits and vegetables, according to the University of California.
Types of Sulfur Spray
West Virginia University notes that there are several types of sulphur sprays for apple trees, including liquid lime-sulphur, dry wettable sulphur and flowable sulphurs. There is a granulated form of sulphur as well, but it is not appropriate for spraying.
When Sulfur Spray is Used
Application of sulphur spray on apple trees takes place beginning when the trees are just starting to leaf out and may continue until harvest or the end of August, according to the Michigan State University Extension.
Even though sulphur sprays are organic, they can still be caustic and irritating to eyes and skin. Inhalation of sulphur mist should be avoided. Read all mixing, spraying and storage instructions carefully, and pay close attention to safety precautions.
Toxicity to Beneficial Insects
Sulphur is toxic to many beneficial insects that are natural predators of insects and mites that can damage apple crops.