Peach leaf curl is a common disease affecting stone fruit, particularly peaches and nectarines. Caused by a fungus, it attacks newly forming leaves in the spring, leading to distorted and premature foliage drop. This disease can weaken a tree and severely reduce fruit production.
Visual Identification of Peach Leaf Curl
Peach leaf curl becomes obvious shortly after the leaf buds open in the spring. The most noticeable sign is a dramatic distortion of the new foliage. Infected leaves become thickened, puckered, and severely curled, often appearing deformed or blistered.
The color of the affected leaf tissue shifts from pale green to striking shades of red, purple, or yellow. These areas feel thick and somewhat rubbery due to the abnormal growth stimulated by the fungus. The infection may also cause young shoots to become thickened, stunted, and distorted, and in severe cases, the fruit itself can develop reddish, warty bumps.
Later in the season, the distorted areas may develop a grayish-white, powdery coating, which is the fungus producing its spores. These infected leaves eventually turn brown and fall off the tree, sometimes leading to substantial defoliation. The tree often responds by growing a second flush of leaves, which typically appear normal once warmer, drier weather arrives.
The Fungal Pathogen and Its Infection Cycle
The specific cause of peach leaf curl is the fungus Taphrina deformans, which is active during the dormant and early growing seasons. This fungus survives the winter as yeast-like spores, known as blastospores, lodged on the rough surfaces of the bark and under the scales of the buds. They remain inactive until conditions favor infection.
The infection process depends on cool, wet weather coinciding with bud swelling and bud break. Rain is necessary to wash the overwintering spores from the bark into the opening buds where new leaf tissue is developing. Optimal conditions occur when temperatures are between 50°F and 70°F, especially when wetness persists for more than 10 hours.
Cool spring temperatures slow down leaf development, extending the length of time they remain susceptible to infection. Once the leaves have fully emerged and expanded, they are no longer vulnerable to the fungus. This narrow window explains why the disease is only seen on the first set of leaves to emerge each spring, while subsequent new growth remains healthy.
Management and Control Strategies
Effective management of peach leaf curl relies on preventive measures applied before the symptoms appear. Treatment is ineffective once the leaves are infected, as the fungus has already entered the plant tissue. Prevention focuses on eliminating the overwintering spores on the tree surfaces before they can enter the buds.
Chemical control involves applying a preventative fungicide during the dormant season. The ideal timing for this application is in the late fall after all the leaves have dropped or in the late winter/early spring before the flower buds begin to swell. Common fungicides used include copper-based products and chlorothalonil.
Thorough coverage of the entire tree—including all branches, twigs, and buds—is necessary for the fungicide to be effective. In regions with high rainfall, a single application in the fall, followed by a second application in late winter before bud swell, may be recommended to ensure protection.
Cultural control methods also support tree health and resistance. Selecting resistant varieties, such as ‘Frost,’ ‘Indian Free,’ or ‘Oregon Curlfree,’ is a long-term approach that minimizes the need for chemical sprays.
Additionally, removing and disposing of infected fallen leaves and fruit reduces the amount of fungal material available to overwinter in the area. Providing the tree with adequate irrigation and fertilization after a severe infection helps the tree recover and produce a second set of healthy leaves.