Gardening: Battle plant diseases with science

Nancy Szerlag
Special to The Detroit News

If our growing season dominated by cold, wet weather has taken its toll on your ornamentals and edibles, take heart — you are not alone. In many gardens the leaves of trees, shrubs and perennials are covered with dots and spots and tomatoes are taking forever to grow and ripen.

Nighttime temperatures around 60 degrees and high humidity is the perfect setting for powdery mildew, the most common fungal disease. It starts as small white or gray fuzzy spots and quickly spreads to cover the leaves. Treating with a fungicide will control further growth of the fungus, but will not undo the damage to the leaves, so preventative spraying is the key keeping your garden looking good.

I opt not to use chemical fungicides in my landscape because of their possible effects on toads, frogs, birds, bees and butterflies. However, the OMRI listed organic fungicide Actinovate (, containing the patented beneficial microorganism Streptomyces lydicus, which attacks a variety of fungal diseases including powdery mildew in the lawn and garden including root rot, black spot and rusts, is a good option. When used as a protectant, prior to infection, Actinovate is also labeled for use against the infection of the lethal disease downy mildew that attacks cucumbers, zucchini and tomatoes.

A 2 oz. packet of Actinovate, priced under $15, will treat 550 plants or 5,000 square feet of lawn and is available independent garden centers, Uncle Luke’s in Troy and Plant Natural online (

For those who eschew the use of any commercial products in their gardens, the age-old home remedy of spraying with milk may be the perfect solution to warding off powdery mildew. Scientific testing in Australia and Brazil has proven that a mix of milk and water at a rate of 1 part milk to 9 parts water is effective when used on grape vines and zucchini. A few drops of liquid dish soap, such as blue Dawn, will act as a spreader sticker. This formula will also work on pumpkins, gourds and other squashes. The secrets to success include spraying the bottoms of the leaves as well as the tops, begin applications before the disease strikes and repeat the applications every 4 to 7 days and after a rain.

When doing a Google search, I found other formulas for milk with higher concentrations. However, too much of a good thing may result in other diseases taking hold, so stick to the scientifically tested formula.

Nancy Szerlag is a master gardener and Metro Detroit freelance writer. Her column appears Fridays in Homestyle. To ask her a question go to and click on Ask Nancy. You can also read her previous columns at