Ferroglobulin

The presence of ferroglobulin in milk is perhaps the explanation for the ability of this product to treat powdery mildew in the garden. Milk is diluted with water (typically 1:10) and sprayed on susceptible plants at the first sign of infection, or as a preventative measure, with repeated weekly application often controlling or eliminating the disease. Ferroglobulin produces oxygen radicals when exposed to sunlight, and contact with these radicals is damaging to the fungus.[1]

Ferroglobulin is a protein in whey.