If you have peach or nectarine trees, winter is the time to spray them to prevent peach leaf curl.

Peach leaf curl is a fungal disease that attacks peaches and nectarines. It appears in spring, causing new leaves to become reddish, puckered and severely distorted. This disease is caused by the fungus Taphrina deformans and is one of the most common disease problems for backyard peach and nectarine trees here in Butte County. In addition to disfiguring leaves, leaf curl can affect the blossoms, stems and fruit of infected trees. If it is severe enough, leaf curl can significantly weaken a tree and reduce fruit production. Leaves affected by leaf curl fall off in the spring, exposing the main limbs to sunburn injury. And sunburn injury facilitates flatheaded borer attacks, which often result in limb dieback.

The leaf curl fungus survives the hot, dry summer months as spores on the tree surface. Then, with the cool, moist weather of winter and spring, the spores germinate and the fungus resumes growth, attacking immature leaves as soon as buds begin to break (swell and crack), and later as leaves and shoots emerge from buds.

The best way to avoid leaf curl is to use resistant varieties of peaches and nectarines. Resistant peach varieties include Frost, Indian Free, Muir and Q-1-8. Although the Frost peach variety is very resistant to leaf curl, it must receive fungicide applications its first two to three years of growth. Redhaven peach and most of the varieties derived from it are rated “tolerant” to leaf curl. On the other hand, Redskin peach and its cultivars are rated “susceptible to highly susceptible” to the disease. Kreibich is a nectarine variety that is resistant to leaf curl.

Nonresistant trees should be treated with a fungicide every year after the leaves have fallen. Generally, a single spraying while the tree is dormant is effective in controlling leaf curl, if applied just prior to bud break.  However, during a particularly wet winter, a second spraying just as the flower buds begin to swell (but before the leaves emerge) is advisable.

The most common fungicides available to the home gardener contain fixed copper. The active ingredient, copper, is listed as “metallic copper equivalent,” or MCE. The higher the MCE, the more effective the product will be. Thorough coverage (by spraying the trees until they are dripping) is essential for disease control. Be aware that repeated use of copper products can result in the buildup of copper in the soil, where it may be become toxic to soil organisms. The synthetic fungicide, chlorothalonil, is the only non-copper fungicide available for managing leaf curl on backyard trees. When using pesticides, always read and follow the label for usage, rates, toxicity and proper disposal. Proper protective clothing and gear (including goggles) should be used when handling any pesticides.

When the symptoms of peach leaf curl appear on a tree in the spring, nothing can be done to control the disease at that time. Removing diseased leaves or shoots does not control the disease. If your tree had leaf curl last spring, be sure to treat it this winter to prevent more serious problems this coming spring.

For more detailed information on this topic, see the University of California Integrated Pest Management (UC IPM) Pestnote #7426, Peach Leaf Curl.

UC Master Gardeners of Butte County are part of the University of California Cooperative Extension (UCCE) system. To learn more about us and our upcoming events, and for help with gardening in our area, visit our website. If you have a gardening question or problem, email the Hotline at mgbutte@ucanr.edu (preferred) or call (530) 538-7201.