Old-time garden wisdom and recent scientific plant research say that milk contains fungicidal properties. Spraying milk on plants will control the growth of bad fungi.
Fungi are microscopic non-green plants; they germinate and grow like other plants. A handful of soil contains thousands and thousands of fungi. There are good fungi and bad fungi. Good fungi help build the soil by breaking down organic matter into nutrients plants can use. Bad fungi are parasites that feed on plants. Bad fungi include mildews (downy mildew, powdery mildew), rusts, rots (root rot, damping off, fruit rot), canker, scab, spot (black spot and anthracnose), wilts (fusarium and verticillium) and smuts (black sooty molds caused by black sooty fungi spores).
Fungicides are preventive, not a cure. They cover plant tissue and do not allow fungi to root.
Plant researchers in Brazil and Australia using milk as a fungicide on vegetable crops, grapes, and flower crops found that spraying a dilute mix of 1 part milk and 9 parts water prevented fungi from growing.
The researchers also believe that the potassium phosphate in milk helps boost the plant’s immune system and may also work as an antibiotic.
A note: skim-fat milk works best; the fat in whole milk may clog up your sprayer. Even reconstituted powdered milk will work.
Tomato disease fighter formula: combine 1 part skim milk and 9 parts water. Spray the plant every two to three weeks until mid-summer (most fungal diseases have run their course by mid-summer, except where the weather stays warm and humid).