Besides reducing the need for harsh chemicals in the garden, natural fungicides have a few other benefits. Firstly, gardeners can often make natural fungicides from things they already have around the kitchen, making them very convenient. The ingredients in homemade, natural fungicides often also cost very little money. Additionally, natural fungicides do not harm beneficial soil organisms or bees, like commercial fungicides sometimes do.
Baking soda helps prevent fungal diseases. It also kills existing fungal spores on plant leaves. Gardening Australia expert Jerry Coleby-Williams recommends mixing a drop of vegetable oil, a drop of natural detergent and 2 tsp. of baking soda in a liter of water to make a natural fungicidal spray. The baking soda kills fungus, and the detergent and oil help the spray stick to plant leaves. This mixture kills powdery mildew, black spot and rust on roses, tomatoes, Chinese celery and other plants with soft leaves.
Both the National Gardening Association and Gardening Australia experts recommend a solution of 1 part milk in 10 parts water as an anti-fungal treatment. To use the solution, put it in a spray bottle and spray it over all of the plant surfaces. Raw and organic milk works best because it has natural antibiotic properties that pasteurization and antibiotics fed to cows can destroy.
Montana Federation of Garden Clubs recommends introducing the beneficial fungus, Gliocladium virens, to a garden's soil to prevent plants from rotting (See Reference 3). This fungus occurs naturally in soils, and adding some extra Gliocladium virens protects plants from fusarium rot and pythium rot. The natural bacteria, Bacillus subtilis, also prevents fungal problems and controls existing plant diseases. Some natural fungicide sprays contain this bacteria, which helps kill powdery mildew, botrytis, blight and fire blight.
Natural Horticultural Oils
Most horticultural oils come from refined petroleum products, but the National Gardening Association explains that gardeners can also use natural horticultural oils made from vegetable oils or neem oil. Horticultural oils rubbed or sprayed on plant leaves control powdery mildew and also prevent many insects from spreading fungal spores, like aphids and whiteflies.