At this time of year most people are not thinking about next year’s fruit crop, but to be successful with peaches and nectarines, the critical time is now. There is a particularly obnoxious foliar disease commonly called “peach leaf curl (PLC)”, caused by a fungal pathogen, Taphrina deformans. This fungal foliar affliction can defoliate peach and nectarines on both ornamental and fruit bearing trees. This fungus is responsible for creating strange and weird contorted, puckered up, yellow to red to purplish, deformed leaves. Strangely enough, the PLC fungus can also infect young, green twigs or shoots causing swollen, stunted, and sometimes chlorotic shoots with curled leaves at their tips.
Symptoms of peach leaf curl fungus, Taphrina deformans, on peach leaves
The infected leaves develop multiple raised, blister-like lesions on their surface. These lesions will eventually turn a powdery, grayish-white or yellow-brown before the entire leaf declines, turns yellow and drops off the tree. Once infected leaves drop, the disease does not spread further during the current growing season! The fallen leaves turn brown and those infected, blistered leaf areas will produce powdery gray spores. These spores are blown by winds to peach twig surfaces and remain there for the winter.
Potential impact of Taphrina deformans fungus, commonly called peach leaf curl, on susceptible peach leaf leaves
Spores of the PLC fungus overwinter on the surface of twigs, in bark crevices and on the bud scales of peach and nectarine trees. In spring, these overwintering spores multiply during periods of cool, moist weather. Spores are dispersed over tree surfaces on a film of water, to ultimately cover and move into the swelling buds. This coincides nicely with peach leaf and fruit buds developing and beginning to swell at a microscopic level.
Potential impact of Taphrina deformans fungus, commonly called peach leaf curl, on susceptible peach leaf leaves image
Those same cool conditions will slow foliar expansion, allowing additional time for fungal infections to occur on developing leaf tissue. Rain is necessary for PLC fungal infections to occur; conversely, dry weather during bud break and subsequent bud swelling, limits PLC infections. Peach leaf curl fungal infections typically occur on new, tender plant tissues during bud swell and 50° to 70°F are optimum for infections to occur.
Peach leaf curl fungal infections from Taphrina deformans beginning to kill peach leaves image
Peach leaf curl is a common disease of peach and nectarine trees throughout the Midwest and eastern United States. Where the disease is severe, both fruit yield and quality are reduced but overall tree vigor is also impacted because of the early loss of leaves. PLC is often very prevalent after relatively mild winters, due to an increased survivability of the overwintering fungal spores. This is why control measures, such as dormant season fungicide applications, must thoroughly cover all branches and twigs to kill the overwintering spores before bud swell in the spring.
Peach leaf curl fungal infections from Taphrina deformans causing leaf death on peach image
The PLC fungus is not difficult to control... however, TIMING is EVERYTHING! A single fungicide application using chlorothalonil or a “fixed copper” fungicide, made in the fall after leaves have dropped or in spring before bud swell, will control the disease. If you wait until spring, the application must be made before bud swell and in my humble opinion, that is next to impossible to achieve. If spring applications are to be made, temperatures must be closely scrutinized throughout the entire overwintering months right up until the application. Unusually warm weather during late winter months often encourages bud swell, resulting in fungicide sprays for PCL being ineffective. Once the fungus enters the leaf, the disease cannot be controlled.
Peach leaf curl fungal infections from Taphrina deformans causing leaf death on peach image
Fixed copper products include the basic copper sulfate, copper hydroxide, and copper oxychloride sulfate (C-O-C-S); however, those easy to mix and easy to apply liquid products (e.g., Kop R Spray Concentrate® [Lilly Miller], Liqui-Cop® [Monterey], Captain Jack’s Copper Fungicide® [Bonide] are not always available. Bordeaux mixture can be used also but may burn young succulent leaf tissue if not applied as a dormant spray. Bordeaux should not be prepared/mixed up early before the actual spray application and not be immediately used. If mixed and left standing unused, the actual chemical composition changes over time. This chemical breakdown is not only irreversible, but it results in a loss of fungicidal efficacy and causes the formation of larger, dense, crystalline particles, which clog spray nozzles!
Peach leaf curl fungal infections from Taphrina deformans causing extreme blistering and leaf collapse image
Peach leaves infected by the Taphrina deformans fungus begin appearing in mid-to late May and are easily distinguished from healthy leaves in that they are puckered and thicker than normal. The most effective method to manage the PCL fungus is to spray the tree with a dormant season fungicide (lime sulfur, copper fungicide or chlorothalonil) just after the leaves have fallen in late fall or early winter! Don’t put it off until Spring, save next year’s peach leaves NOW… Get out there and spray today!!