Peach leaf curl caused by the fungus, Taphrina deformans, is a common disease of peach and nectarine. This fungus destroys young peach leaves. New leaves will develop, however, their growth reduces established food reserves, weakens the tree, and may reduce yield. Defoliation by peach leaf curl in successive seasons may kill the tree.

Symptoms
Infected leaves, which begin appearing in mid-May, are easily distinguished from healthy leaves in that they are curled, puckered and thicker than normal. Deformed areas are red to yellow at first and then turn brown. Eventually the infected leaves fall from the tree.

Symptoms of leaf distortion caused by the fungus, Taphrina deformans

When trees are severely infected by the fungus, peach fruit can also become susceptible. Infected fruit exhibit distorted, warty growths on the surface and will usually abort.

Disease Cycle
Spores of the leaf curl fungus overwinter on the surface of peach twigs. In spring, the spores multiply during periods of moist weather until the leaf buds swell and open. Rain is necessary for infection. The spores are carried on a film of water into the buds, where leaves are infected. Cool, wet weather slows leaf development and allows more time for leaf curl infection. Infection occurs readily at 50 to 70 degrees F. Dry weather during bud swell and bud break limits leaf curl infection. After the deformed and discolored leaves turn brown and fall, they produce powdery gray spores. These are blown by winds to peach twig surfaces and remain there for the winter.

Disease Management
Certain cultural practices assist in the management of peach leaf curl. Where leaf curl is severe, it is very important to maintain tree vigor by: (1) thinning fruit to reduce demand on the tree, (2) irrigating to reduce drought stress, and (3) fertilizing trees with nitrogen by June 15. Be careful not to overstimulate trees. Redhaven and most cultivars derived from Redhaven are more resistant to leaf curl than Redskin and cultivars derived from Redskin. Peach leaf curl is not difficult to control chemically. A single fungicide application made in the fall after leaves have dropped or in spring will control the disease. The spring application must be made before bud swell. Once the fungus enters the leaf, the disease cannot be controlled. The fungicide kills the spores on twig surfaces. Applications must be thorough for either the spring or the fall spray to be effective. Complete coverage of the twigs, branches, and trunks is essential. Secondary infections do not occur after the initial infections. The disease does not spread later in the season.