Winter is a key time for gardeners to take preventive actions against peach leaf curl in some areas in California. Caused by the fungus Taphrina deformans, peach leaf curl causes distortion, thickening, and reddening of foliage as peach and nectarine trees leaf out in the spring. Damaged leaves often die and drop, but they will be replaced with new, healthier leaves once the weather turns dry and warm. An untreated leaf curl infection will contribute to a tree's decline over several years.
To prevent peach leaf curl in areas where the disease occurs, treat susceptible trees with preventive fungicides during the dormant season, ideally in late November or December. A second application should be made in late winter or early spring just before buds swell. In some places, a third treatment may be necessary. Treatment isn't effective if applied after symptoms appear. Removing affected leaves or shoots will not reduce the problem. A few peach varieties are resistant, including Frost, Indian Free, Muir, and Q-1-8.
Dormant Treatment Materials
When lime sulfur and tribasic copper sulfate were removed from retail shelves, the choices of fungicides available against peach leaf curl for home gardeners became limited. Copper ammonium complex (Liqui-Cop or Kop-R-Spray) is less effective than discontinued formulations, but can be made more effective by applying it with 1% horticultural oil in the solution. Copper soap (copper octanoate) may also provide some protection.
The fungicide chlorothalonil (sold as Daconil, Ortho Garden Disease Control, and others) is effective, but care must be taken in handling it since it causes severe eye or skin irritation and is a likely carcinogen. Proper protective care, clothing, and equipment should always be used.
Bordeaux mixture, which gardeners can mix up themselves, is also effective, but preparing it takes time and planning. The ingredients needed to make Bordeaux mixture are powdered copper sulfate in “bluestone” form, and hydrated lime (calcium hydroxide) or quick lime (calcium oxide). Be sure customers have goggles, gloves, and a dust and mist-filtering respirator to use while working with hydrated lime and mixing up the solution.
For more information, see the UC IPM Pest Notes Peach Leaf Curl.