If you have peach or nectarines 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 early spring, causing young leaves to turn red, wilt and become severely distorted. The 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 distorting leaves, leaf curl can affect the flowers, stems and fruits of infected trees. If it is severe enough, leaf curl can significantly weaken a tree and reduce fruit production. Leaves affected by leaf curl drop in early spring, leaving the main organs affected by sunburn. And sunburn injuries tend to facilitate flat piercing attacks, often resulting in limb death.
Leaf curl fungus survives in the hot, dry summer months as spores on the surface of the tree.
Then, with the cool, moist weather of winter and spring, the spores germinate and the fungus resumes growth, attacking immature leaves as soon as the buds begin to break (swell and crack), and later when the buds begin to break. Leaves and shoots emerge.
The best way to avoid leaf curl is to use resistant varieties of peaches and nectarines.
Resistant varieties of peaches include Frost, Indian Free, Muir and Q-1-8. Although the Frost Peach variety is very resistant to leaf curl, it should receive fungicide applications within its first two to three years of growth. Red Haven peaches and most varieties derived from it are rated “tolerant” for leaf curl. On the other hand, the red skin peach and its varieties have been rated as “highly susceptible to susceptibility” to the disease. Krebich is a nectarine variety that is resistant to leaf curl.
Non-resistant trees should be treated with a fungicide every year after the leaves have dropped. Generally a single spray while the tree is dormant is effective in controlling leaf curl if applied just before bud break. However, during particularly wet winters, a second spray at the time of flowering (but before leaves emerge) is recommended.
The most common fungicide available to the home gardener contains fixed copper. The active ingredient, copper, is listed as “metallic copper equivalent,” or MCE. The higher the MCE, the more effective the product. Thorough coverage (spraying till the trees drop) is essential for disease control. Keep in mind that repeated use of copper products can lead to a build-up of copper in the soil, where it can be toxic to soil organisms. The synthetic fungicide, chlorothalonil, is the only non-copper fungicide available for the management of leaf curl on backyard trees. When using insecticides, always read and follow the label for usage, rates, toxicity and proper disposal. Appropriate protective clothing and gear (including goggles) should be used when handling any insecticide.
When symptoms of peach leaf curl appear on a tree in spring, nothing can be done to control the disease. Removal of diseased leaves or twigs 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 University of California Integrated Pest Management pestnote number 7426 on Peach Leaf Curl Management Guidelines at ucanr.edu.
Butte County’s UC Master Gardeners are part of the University of California Cooperative Extension System, serving our community in a variety of ways, including 4-H, agricultural advisory, and nutrition and physical activity programs. To learn more about UCCE Butte County Master Gardeners, and help with gardening in our area, visit https://ucanr.edu/sites/bcmg/. If you have any gardening questions or issues, call the hotline at 538-7201 or email [email protected]