Peach Leaf Curl
Peach leaf curl is a disease caused by the fungus Taphrina deformans. The fungus is specific to peaches and nectarines and can infect leaves and immature fruit. The disease occurs during cool wet weather at the time of leaf emergence and expansion. The fungus is present almost anywhere peaches are grown, but usually goes unnoticed during years in which it is warm and dry during the period from bud swell to leaf expansion. Due to the weather conditions in spring 2011, the disease was more common than usual in Utah peach orchards.
The fungus survives as blastospores on the bark of peach trees and near buds. During wet weather the spores are washed onto emerging leaves. The spores germinate and penetrate the leaves, inducing the distorted blister-like deformation. Taphrina deformans does not produce fruiting bodies. It forms a single layer of asci (sac-like structures that contain sexual spores) on the surface of discolored and distorted leaf areas. It is sometimes visible as a dusty cover on the leaves. The spores are released and are blown to the bark of trees where they survive during the summer. The sexual spores eventually germinate and produce blastospores. The blastospores multiply by budding (similar to yeast) and are washed onto new emerging leaves in the spring.
Taphrina deformans induces cells on the margins of infected leaves to multiply rapidly and randomly, resulting in deformation and curling. The infected distorted leaf parts are often yellow or red colored. Infected leaves eventually turn brown and fall off. Infected fruit may drop early or show wart-like symptoms when mature. The tree will leaf out to replace the fallen leaves, which can affect tree vigor and yield.
Infections occur only during temperatures between 50° and 70°F. Disease incidence is highest and most noticeable during wet conditions. During cool temperatures, expansion of young leaves is slower, allowing for a longer infection period. At higher temperatures, infection may occur, but symptoms will not develop due to faster expansion of the leaves. Once leaves have fully expanded they become resistant.
There are no management options after infection has occurred. Chemical management can be done in the fall with a single application of copper or chlorothalonil (both available for commercial and backyard plants). Cultural practices that can be used by homeowners include raking and removing leaves in the fall to remove as much inoculum as possible and using resistant varieties.
-Claudia Nischwitz, Plant Pathologist