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. 

Why Milk?

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. 

Several seasons back, Jeff McCormack, Ph.D., founder of Garden Medicinals and Culinaries and Southern Exposure Seed Exchange, shared a tomato pruning method with me that delays the onset of early blight, and reduces the number of leaves lost in the course of the season.

Extension publications often suggest pruning tomatoes to prevent disease by improving air and light penetration. Jeff's method concentrates pruning at the base of the plant by removing leaves that eventually will be lost to early blight anyway. When the lowest leaves are removed just as the first leaf spots appear, you also remove millions of spores. And, because the bases of pruned plants dry quickly, the spread of the disease is slowed because early blight fungi need damp leaves in order to germinate and grow.

What's Early Blight?

The most common leaf-spot disease of tomato, early blight (Alternaria solani) fungi cause leaf spots to form on tomato leaves. Inside irregularly-shaped dry patches (which often have yellow margins), look for small dark rings. These are the fruiting colonies.  The grayish powder inside the dark rings are the spores, which splash or blow onto new leaves to form new spots. When spots become numerous, entire leaves wither to brown.

Commercially-grown tomatoes are often sprayed weekly with fungicides to suppress early blight. Organic growers sometimes use copper fungicides, which are often effective, but frequent use may harm earthworms. A few resistant varieties have been developed, but some failed to perform well in field trials, and others fall short in terms of flavor and texture.

Preventive Pruning

With big indeterminate varieties, prune or nip out all leaves that hang within 1 foot of the ground. If you see numerous lesions on the pruned leaves, you can go higher, to 18 inches. See the before and after photos below.

With stocky indeterminate varieties, trim out most of the leaves that touch the ground, but don't get carried away. If the plants have already set a heavy load of fruit, I also trim off some of the newest blossom clusters to keep the fruit:leaf ratio high. See the before and after photos below.

In addition to pruning, drip irrigation discourages early blight because the plants can be watered without wetting the leaves. Mulch after the plants are pruned to retain soil moisture.

Early blight starts with a few small lesions, but quickly spreads in damp summer weather. Eventually, the lower halves of infected plants wither to brown.

Before: Vigorous indeterminate tomatoes usually begin to show early blight symptoms just as they load up with green fruits.

After: Pruning off low leaves eliminates the damp environment early blight needs to spread, which reduces the number of leaves lost later in the season.

Before: Stocky determinate varieties that grow close to the ground are often hit hard by early blight just as the fruits begin to ripen.

After: When pruning determinates, take only the leaves that touch the ground. You can also prune off a few blossom clusters to help keep the leaf:fruit ratio high, which insures good flavor.

— Photos by Barbara Pleasant