Infected leaves, which begin appearing in mid-May, are easily distinguished from healthy leaves because they are curled, puckered, and thicker than normal. Deformed areas are red to yellow at first and then turn brown. The infected leaves eventually fall from the tree.
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°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, Chemical
Peach leaf curl is not difficult to control. A single fungicide application, made in the fall after the leaves have dropped or in the spring before bud swell, will control the disease. The spring application must be made before budswell. Once the fungus enters the leaf, the disease cannot be controlled.
The fungicide kills the spores on twig surfaces. For either the spring or the fall spray to be effective, application must be thorough. 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.
Disease Management, Cultural
Where leaf curl is severe, it is very important to maintain tree vigor by
- thinning fruit to reduce demand on the tree;
- irrigating to reduce drought stress;
- fertilizing the trees with nitrogen by June 15.
Be careful not to overstimulate the trees. Redhaven and most varieties derived from Redhaven are more resistant to leaf curl than Redskin and varieties derived from Redskin.