It happens every summer. Just as your beautiful cherries, peaches, plums or grapes start to ripen, disaster strikes. As the disease called brown rot takes over, fruits become covered with a powdery brown coating as they quickly rot and shrink into mummies.
Some varieties are more susceptible than others, but what can you do when you have high-risk fruits that are trying to bear a good crop? Organic growers use sulfur sprays, but frequent use can cause problems in the soil. This year I tried a newer natural method, which involves spraying a dilute milk-and-water solution to suppress brown rot to acceptable levels. It could be a single-season fluke, but my experiment has been a resounding success.
In 1999, a team of Brazilian researchers found that weekly sprays of a milk solution controlled powdery mildew in zucchini squash. In more recent studies, milk or whey-based sprays were as effective as fungicides in controlling powdery mildew in two plantings of wine grapes in Australia. Plant pathologists suspect that as compounds in dairy products interact with sunlight, they cause crippling damage to powdery mildew fungi and spores. If milk works on powdery mildew, I thought it might help with brown rot, which has a similar life cycle.
My subjects were a mature 'Stanley' prune plum and a mature planting of 'Concord' grapes – both easy targets for brown rot and other fungal diseases. In the past, the plum crop was often lost entirely to brown rot, and the grapes typically had half of their fruit ruined by brown or black rot.
Using a hand-held compression spray bottle, I applied a spray using this recipe:
one-half cup organic low-fat milk
1 quart warm water
3 drops dishwashing liquid (to help the mixture stick)
Beginning in early July, I sprayed the plants five times at two-week intervals. I sprayed in the mornings, covering the fruits and foliage until the spray mixture dripped to the ground. I stopped spraying when the fruits began to ripen, because I didn't want milk residue on the fruits.
The results? Less than 10 percent disease incidence on the plum, and less than 30 percent on the grapes – both huge improvements over past seasons.
I'll repeat the method next year, but meanwhile it would be great to hear from other gardeners who have tried milk on other disease problems. Did it work for you as well as it worked for me?
Above: Despite two days of steady rain, ripe 'Stanley' plums did not turn into fuzzy shrunken mummies.
Left: Regular milk sprays suppress powdery mildew on grape foliage, and may help defend fruit from brown rot and black rot, too.
Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website or finding her on Google+.