Baking soda has a profusion of uses, and one of them is as a natural fungicide in the garden. It's especially effective at ridding roses of black spot and treating blight and powdery mildew. Dissolve 1 tsp. of baking soda in 1 qt. of water. Add the mixture to a clean spray bottle and thoroughly spray the affected plant, including the undersides. A dash of mild or castile soap added to the baking soda fungicide helps it spread more evenly.
Plants suffering from mildews and leaf spot may find relief from garlic oil fungicide. Mince a bulb of garlic and infuse in 1 to 2 oz. of olive oil for a minimum of 24 hours. Set the garlic oil in a warm, sunny location during the infusion process. Strain the garlic. Fill a clean spray bottle with water and add 1/4 oz. of castile or mild soap and the garlic oil fungicide. Spray the affected plant areas thoroughly. For use on sensitive ornamentals, test-spray a small area. If no leaf damage shows within two or three days, proceed with spraying the rest of the plant.
Neem oil, extracted from the neem tree, has antifungal properties that make it an effective organic fungicide for rust, scab, mildew and black spot. Mix 2 tbsp. of neem oil with 1 gallon of water. Shake the neem oil fungicide thoroughly and spray the plant surfaces until they are completely wet.
Apple Cider Vinegar
Just like baking soda, apple cider vinegar is used for a multitude of purposes. Use it to treat scab, leaf spot, mildew and black spot on roses. Mix 3 tbsp. of apple cider vinegar with a gallon of water and shake thoroughly. Use out of direct sunlight and spray on all affected areas of the plant.
Farmers have used sulfur for thousands of years to prevent fungi, and it still has a place in the organic gardener's garden. Fungal spores cannot germinate in a sulfur film, so while sulfur does not actually kill fungi, it does prevent it from forming. Sulfur has a tendency to wash away easily, so frequent applications may be necessary in wet conditions, which produce fungi. Sulfur is especially useful in preventing brown rot, leaf spot, powdery mildew and scab on crops like grapes, potatoes, tomatoes, strawberries and tree fruits. Sulfur is sold in liquid and powder form. Powdered sulfur adheres better to plant surfaces, while liquid sulfur is easier to apply. Follow the directions on the back of the product for proper application.