Phytophthora blight is a soil-borne fungal disease in the home garden. If unchecked, it causes root, stem, and fruit rot. Rhododendrons, azaleas, skip and cherry laurels, arborvitae, Leyland cypress, dogwood, cherry, and redbud — even large trees such as maples and oaks — all are susceptible to phytophthora. It strikes even young trees, and the older a tree gets, the more susceptible it becomes. Once infected, trees or plants can eventually die. 

At John B. Ward & Co., we combat this destructive garden invader with a product called potassium phosphite. In the 1970s, French scientists screening various chemicals for fungicidal properties discovered that potassium phosphite had multiple applications. Not only can it be used as a fertilizer, it also works as a fungicide. And unlike most fungicides, which move in just one direction — up — in a plant, potassium phosphite moves in both directions. This mode of action is invaluable in treating fungus diseases — including phytophthora. 

In the past, I’ve described this product to clients as working “like a steroid.” More precisely, according to Dr. Peter Landschoot of Penn State University, it can best be compared to a short-term vaccination. By creating a response to the infection, or something that may mimic the infection, it works the way a vaccine works to stimulate antibodies. 

As spring approaches, watch for the signs of phytophthora in your yard. If the leaves of trees or plants turn dull green or yellow, or some cases red or purplish, call us. It may be time to begin treatment for phytophthora.