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• Anti-transpirants, which are normally used to protect plants from drying out, are also believed to work to control fungus by coating the leaves with waxes, plastic polymers, or silicones, that prevent fungal spores from infecting leaves.
• A mixture of baking soda, horticultural oil, and water can help control powdery mildew. This homemade fungicide also reduces or eliminates black spot to acceptable levels on resistant rose varieties. Mix one rounded tablespoon of baking soda (sodium bicarbonate) and one tablespoon of horticultural oil per gallon of water, and spray on a weekly basis (and again after a heavy rain). To avoid burning the leaves, make sure plants are well hydrated and spray early in the morning. Do not apply during hot weather. You can also buy commercial formulations that use potassium bicarbonate, which is more effective than sodium bicarbonate for powdery mildew control.
• Sulfur-based fungicides have long been the organic gardener's weapon of choice for battling fungal diseases. Just don't use them when temperatures exceed 90° F.
• Whole neem oil can control black spot, powdery mildew, and rust as well as many insects and mites. (Neem oil comes from the tropical neem tree, Azadirachta indica.) Neem is also less harmful to beneficial insects, than chemical insecticides.
• Bacillus subtilis is a recently discovered bacterium that attacks fungi that cause diseases such as powdery mildew and black spot. Use it as preventive spray and to control existing infections.

• Water. Nothing fancy here, just plain old water. A strong spray from the hose can knock aphids, spider mites, and other pests off plants. Spray in the morning so leaves have a chance to dry during the day.
• Bt (Bacillus thuringiensis) is a microbial insecticide that kills only moth and butterfly larvae and is harmless to most other insects and animals. However, it won't discriminate between pest caterpillars and those of desirable butterflies.
• Horticultural oil, or "summer" oil, control a wide variety of pests such as rose scale, whitefly, aphids (and their eggs), and spider mites. Don't use horticultural oils when you expect temperatures to rise above 90° F.
• Insecticidal soaps. These specially formulated soaps are a key element in any least toxic pest-control strategy. They're effective against a wide range of pests, particularly soft-bodied insects such as aphids, immature scale, leafhoppers, mites, thrips, and whiteflies.