BLUE SPRINGS, Mo. - Leaf curl is a troublesome disease of peach, nectarine and related plants. "Leaf curl is worse when the weather is cool and wet," said Lala Kumar, University of Missouri Extension horticulture specialist. Leaves infected with the fungus Taphrina deformans become thickened, curled and grossly deformed or puckered. As the disease progresses, the leaf gradually changes color to light green, gray and yellow. Early leaf drop results in poor growth and yield.

The spores of this fungus survive the winter on bark and buds. The spores then infect the buds in the spring as they begin to swell and new leaves emerge. The host tree tissues are susceptible for a short period in the spring. As the tissues mature, they become resistant to this disease. "Thus, timing is critical for disease control," said Kumar.

Leaf curl can be easily controlled with a single fungicide application. Trees can be sprayed in the fall after leaf drop or an application can be made in the early spring before bud swell. Fungicides that can be used to control this disease include Bordeaux mixture, liquid lime sulfur and chlorothalonil. Thoroughly cover the bark and trunk of the trees when applying fungicide. In very wet seasons and when disease has been severe, two to three spray applications will be needed at seven day intervals.

If leaf curl results in significant defoliation in the spring, the fruit on affected trees should be thinned to compensate for the loss of leaves. Over-cropping the tree will weaken it and make it more susceptible to winter injury.

For additional information, you can download the MU Extension guide "Fruit Spray Schedules for the Homeowner" (G06010) or you can visit the Ask a Missouri Master Gardener page on Facebook.