Issue 7, June 8, 2015

Peach Leaf Curl

Recently, there have been a number of requests for information on how to control peach leaf curl, a disease caused by the fungal pathogen Taphrina deformans.  Peach leaf curl is one of the most common diseases of peach and nectarines in home plantings. This disease also occurs in commercial orchards, but is much less common due to the frequent use of fungicides. A number of other Taphrina species are known to cause several common diseases in the landscape including oak leaf blister and plum pockets.

Peach leaf curl causes infected plants to produce severely distorted leaves with thickened, puckered, and curled areas covering nearly the entire leaf. Affected tissues are initially light green, but eventually develop red and purple tints before transitioning to yellow or brown in color. Infected leaves drop prematurely, often within several weeks of the initial infection. Defoliated trees develop a second flush of growth by early summer. The resources required to produce the new leaves weakens and stresses the tree, predisposing it to a number of other problems. The good news is that peach leaf curl is a monocyclic disease and will not cause secondary infection to the new flush of leaves.

Taphrina pathogens over-winter in buds and twigs. Infections occur in developing leaves early in spring as the buds begin to swell and continue until the buds are open. Cool spring temperatures slow plant development and allow a longer window of opportunity for fungal infection to occur. Therefore, cool wet springs enable more severe infections.

Unfortunately, once the fungus enters the developing leaf, the disease cannot be controlled. Thus, trees infected with peach leaf curl cannot be treated during the growing season. Instead, mark your calendar as a reminder to apply fungicide during dormant season to protect next year's foliage. A single application in late fall, winter, or very early spring before the buds begin to swell should provide adequate control.  Apply fungicides containing either chlorothalonil or a copper product such as copper octanoate. Before purchasing and using, be sure the product is labeled for use on stone fruits as well as Peach Leaf Curl. Lime Sulfur sprays are also effective, however these products are no longer marketed or registered for homeowner use. Homeowners with existing supplies can continue to use Lime Sulfur products until their supply is exhausted. Please note that Lime Sulfur may cause severe leaf burn if applied to green foliage. (Travis Cleveland)

Travis Cleveland

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