This spring the ISU Plant Disease Clinic has received several inquiries regarding peach leaf curl. Cool, wet, humid weather is perfect for the fungus Taphrina deformans to infect and produce disease symptoms.
Diseased leaves become thick and puckered with a red or purple hue. As the disease progresses, a powdery film of spores forms on the leaves giving them a gray cast. The deformed leaves will turn yellow or brown and fall from the tree. There is only one cycle of infection during the growing season, so once the leaves fall there won't be any new infection until the following year. The fungus also can infect twigs, flowers, and fruit.
Once symptoms are visible, it's not possible to control peach leaf curl. A single fungicide spray in the fall after leaf drop or in the spring before the buds swell can protect trees from the fungus. Several fungicides, including Bordeaux mixture, liquid lime sulfur, chlorothalonil (Daconil and others), and copper hydroxide are effective for control of peach leaf curl. The fungus survives the winter in infected leaves, fruit, and twigs. Removing plant material that contains the fungus by raking and pruning can reduce the potential for disease the following year. However, heavy pruning can weaken the tree making it susceptible to winter injury.
This article originally appeared in the June 7, 2002 issue, p. 79.