Why are my Peach Tree Leaves Bubbling? Peach leaf curl, also referred to as leaf curl, is a condition caused by the Taphrina deformans fungus. It impacts the blossoms, fruit, leaves, and shoots of peaches, ornamental flowering peaches, and nectarines.
It is a common issue for backyard gardeners in Zone 5-6 who cultivate these trees. The distorted, reddened foliage that it produces is noticeable in the spring, and severe cases can lead to a significant reduction in fruit yield.
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Identification and Harm
At the onset of spring, peach leaf curl manifests as reddish patches on developing leaves. These areas thicken and pucker, resulting in curled and distorted leaves. The thickened regions eventually turn yellowish and then grayish-white as the leaf curl fungus produces velvety spores on the leaf’s surface.
Affected leaves later turn yellow or brown, some remaining on the tree while others fall off. This leads to a second set of leaves developing more normally unless wet weather persists. The defoliation in spring can leave branches exposed to sunburn.
The peach leaf curl pathogen also targets young green twigs and shoots. Affected shoots become thickened, stunted, distorted, and may die. While reddish, wrinkled areas may occasionally appear on fruit surfaces, these infected fruit areas can become corky and prone to cracking as the season progresses.
If left untreated over several years, the tree’s health may deteriorate, necessitating removal.
Infection Life Cycle
Symptoms on leaves typically appear about two weeks after they emerge from buds. The fungus grows between leaf cells, causing them to enlarge abnormally, resulting in swelling and distortion of the leaf. Red pigments accumulate in the distorted cells. Fungal cells penetrate the cuticle of distorted leaves, producing elongated sac-like structures called asci that release sexual spores known as ascospores, giving the leaf a grayish-white, powdery appearance. Ascospores are dispersed in the air, landing on new tissues and germinating to form bud-conidia.
Throughout the hot, dry summer, the fungus survives as ascospores and bud-conidia on the tree’s surfaces. When fall brings cool, wet conditions, ascospores germinate to produce more bud-conidia. The bud-conidia, both old and new, multiply by budding.
A film of bud-conidia forms on the tree’s surface over time. In spring, splashing water from irrigation or rain helps move the bud-conidia to infect new leaves.
The disease thrives during cool, wet periods when leaves are emerging. Optimal fungal growth occurs at 68°F with a minimum of 48°F and a maximum of 79° to 87°F. Bud-conidia budding happens at or above 95% relative humidity. Moisture from rain, dew, or irrigation for over 12.5 hours at temperatures below 61°F is necessary for infection. Prolonged wetness over two days leads to maximum infection. Infection may not manifest if temperatures stay above 69°F, and the disease’s development slows in cool weather.
Peach leaf curl stops progressing when new growth ceases or when the weather becomes dry and warm (79° to 87°F).
Peach Leaf Curl Management
To prevent peach leaf curl, consider utilizing resistant peach and nectarine varieties in gardening Zone 5-6. For nonresistant varieties, apply a fungicide annually after leaf drop, typically in late November in cooler regions and as late as early January in warmer areas.
A single early treatment while the tree is dormant is usually effective, with a potential secondary spray in high rainfall regions or exceptionally wet winters.
Apply the second spray as flower buds start to swell but before green leaf tips emerge.
Resistant Peach Tree Varieties
Several peach varieties exhibit varying levels of resistance to leaf curl. Frost, Indian Free, Muir, and Q-1-8 are currently available resistant options.
The Frost cultivar is notably tolerant but may require fungicide applications in the initial 2 to 3 years.
Redhaven peach and its derivatives are also tolerant to peach leaf curl, while Redskin peach and related options range from susceptible to highly susceptible.
Fewer nectarine varieties show resistance to leaf curl, with Kreibich being a notable exception.
Fungicide Types
Copper
Historically, fixed copper products have been popular among home gardeners for disease control. The metallic copper content, measured as metallic copper equivalent (MCE) on the label, influences product effectiveness.
Various formulations containing basic copper sulfate, cupric hydroxide, or copper oxychloride sulfate are available. Currently, consumer options include liquid products with copper ammonium complex with 8% MCE, enhancing their efficacy. Although a highly effective product with 90% tribasic copper sulfate MCE is no longer widely available since 2010, remaining supplies can still be used.
Copper ammonium complex products can be improved by adding horticultural spray oil, aiding in aphid, scale insect, and mite control. Copper soap fungicides are also on the market and show promise in tree protection.
Note that overusing copper products across multiple seasons can lead to copper accumulation in the soil, potentially harming soil organisms and aquatic life if leached into waterways.
Bordeaux Mixture
Copper sulfate, while less effective alone, can form a potent fixed copper product when mixed with hydrated lime to create Bordeaux mixture.
This concoction proves impactful against peach leaf curl, though it must be prepared immediately before application, as it isn’t commercially available.
Other Fungicides
Chlorothalonil is a synthetic fungicide alternative to copper-based products for managing peach leaf curl in residential settings.
It should be noted, that lime sulfur products are no longer approved for backyard use.
Fungicide Application
When applying fungicides, ensure thorough coverage of the trees to achieve optimal disease control. Pesticide labels should always be consulted for correct usage, rates, toxicity, and disposal instructions. Appropriate protective gear, including goggles, must be worn when handling pesticides.
Physical Controls
While leaf curl symptoms mostly emerge in early spring, little can be done to mitigate the disease during this period. Some gardeners opt to remove diseased leaves or prune infected shoots, but their effectiveness in control remains uncertain. Diseased leaves typically fall off within a few weeks, being replaced by new healthy leaves unless persistent rain occurs.
Severe peach leaf curl cases can hamper tree growth, prompting potential fruit thinning later in the season.
Fall pruning before applying fungicides can reduce overwintering spores and lower the required fungicide amount.
If your trees exhibited leaf curl symptoms in spring, ensure treatment during the subsequent fall and/or winter to prevent significant losses in the following year.
