Peach leaf curl is caused by the fungus Taphrina deformans. Spores are produced on the surface of diseased leaves in midsummer and give the leaf the powdery appearance. These spores are spread by winds and rains, becoming lodged under bud scales and rough bark, and here they remain throughout the summer and winter months. In the spring, when the young peach buds begin to swell, germinating spores of the fungus penetrate the young leaves, causing leaf curl infection.
Peach leaf curl can be prevented by a single spray application made in late fall, after leaf drop, or in late winter, BEFORE bud swell. It is critical that trees be sprayed before buds begin to swell! If buds have begun to swell or open, it is too late to obtain satisfactory control of peach leaf curl as infection has already occurred. Control is impossible once symptoms are visible. Fungicides registered for control of peach leaf curl include liquid limesulfur, chlorothalonil (Daconil, Bravo 720), ferbam, and copper based fungicides (numerous trade names are available) including Bordeaux mixture. Follow all label instructions regarding amounts of pesticide to use, method of application, and safety warnings.
If a dormant spray has been neglected, and disease develops, the fruit on affected trees should be thinned to compensate for the loss of leaves. In addition, fertilize and water trees to help maintain tree vigor — and be sure to get a leaf curl spray on next year!
Ray Ridlen is an agriculture/horticulture educator for the Oklahoma County Extension Service. For more information, call 713-1125.