The control of powdery mildew (Sphaerotheca fuliginia) does not necessarily require the use of expensive fungicides. Recent research by Wagner Bettiol, published in Crop Protection 18(1999) 489-492, indicates that fresh cow milk is effective against powdery mildew on zucchini squash (Cucurbita pepo). Sprays of 10, 20, 30, 40 and 50% milk (by volume in water), applied twice a week until runoff, provided as much control as conventional fungicides. When milk was applied once a week, concentrations of 20 to 50% were necessary to achieve the same level of control as fungicides. When milk concentrations of 30% and higher were used, mold grew on the upper side of leaves but did not appear to harm the plants. Clearly it would make the most sense (economically as well as common sense) to use milk at concentrations between 10 and 30%, where it would be effective but would not result in mold. According to Bettiol, “milk dosages ranging from 3.8 to 19.7% would reduce disease severity by 90%.
Bettiol writes that milk’s effect on powdery mildew may be due to milk’s germicidal properties. The salts and amino acids which it contains have been shown to be effective in controlling powdery mildew. Other ingredients in milk (e.g., sodium bicarbonate) may enhance the plants’ ability to resist stress. Bettiol used fresh whole milk straight from the cow. We do not know whether or not other types of milk (for example, pasteurized or powdered milk) would work equally well. When we asked him, Bettiol said other types should work, but that it is important to use whole milk, which would have a similar composition to fresh milk.