Leaf curl is a troublesome disease of peach, nectarine and related plants, but it 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,” says Lala Kumar, University of Missouri Extension regional horticulture specialist.
Leaf curl is caused by the fungus Taphrina deformans. Infected leaves become thickened, curled and grossly deformed or puckered. As the disease progresses, the leaf gradually changes color to light green, gray and yellow. This is followed by early leaf drop, which results in poor growth and yield, Kumar said.
Spores of the fungus survive the winter on bark and buds. The spores infect buds as they begin to swell and new leaves emerge in the spring. The host tree tissues are susceptible for a short period in the spring. As the tissues mature, they become resistant to the disease.
“Timing is critical for disease control,” he said. Applications of fungicides after bud-break are ineffective.
Fungicides that can be used to control this disease include Bordeaux mixture, liquid lime sulfur and chlorothalonil. All three are available under several brand names. Read the product label carefully, Kumar said.
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 sprays at seven-day intervals will be needed,” he said.
If leaf curl does result in significant defoliation in the spring, thin the fruit on affected trees to compensate for the loss of leaves, he added. Overcropping the tree will weaken it and make it more susceptible to winter injury.
(Source – http://www.farms.com/news/spray-fungicide-in-fall-to-prevent-peach-leaf-curl-99191.aspx)