Infected leaves, which begin appearing in mid-May, are easily distinguished from healthy leaves in that they are puckered and thicker than normal. Deformed areas are red to yellow at first and then turn brown. Photo by K. Peter.
Although new leaves develop, 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.
Infected leaves, which begin appearing in mid-May, are easily distinguished from healthy leaves in that they are 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.
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 (copper or chlorothalonil) application made in the fall after leaves have dropped or in spring before bud swell will control the disease. The spring application must be made before bud swell. If spring applications are made, temperatures must be monitored closely. Unusually warm weather during late winter months can encourage bud swell thereby making fungicide sprays ineffective. 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. Applications made from one side of the tree or with highly concentrated sprays may not be effective.
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, and
- fertilizing trees with nitrogen by June 15. Be careful not to overstimulate trees.