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Peach Leaf Curl

In March and April, garden centers and retail nurseries usually get a large number of questions about peach leaf curl, a fungal disease that only affects peach and nectarine trees.  Distortion, thickening and reddening of foliage as trees leaf out in the spring is its distinctive symptom.  Damaged leaves often die and fall off trees but will be replaced with new, usually healthy leaves.  A leaf curl infection that continues untreated over several years will contribute to a tree’s decline and reduce fruit production.

To prevent peach leaf curl, peach and nectarine trees must be treated with preventive fungicides during the dormant season.  The best time is after leaves have fallen, usually in late November.   In wet climates or during a wet winter, a second application can be made in late winter or early spring just before buds swell.  If the November treatment wasn’t made, it can be applied in January or February before buds begin to expand.

Treatment applied after trees leaf out or after symptoms appear will not be effective.   You will need to advise customers to treat next November.   There is little that gardeners can do to reduce leaf curl in the spring.  Removing affected leaves or shoots will not reduce the problem.   There are a few peach varieties that are resistant or partially resistant to leaf curl.  These are Frost, Indian Free, Muir, and Q-1-8.  Your store may want to feature these varieties for customers who prefer not to apply the dormant spray.

Dormant treatment materials recently discontinued
Two important fungicides used to treat peach leaf curl have been withdrawn from the market.  Lime sulfur (calcium polysulfide) has been cancelled for backyard uses by the U.S. EPA, effective December 31, 2010.  Tribasic copper sulfate (sold as Microcop by Lilly Miller) has been discontinued by the manufacturer (although existing supplies can be sold and used).   As a result, the options for dormant treatments for preventing peach leaf curl in backyard trees are limited and less than ideal.  Copper ammonium complex (Liqui-Cop or Kop R Spray) is still available but is only 8% copper and significantly less effective than Microcop.  It can be made more effective by applying it with 1% oil in the solution. The fungicide chlorothalonil is effective, but is listed as a likely carcinogen and can also cause severe eye or skin irritation if care is not taken in the application process.    Bordeaux mixture, which you can mix up yourself by following the directions in the Pest Note: Bordeaux Mixture, is effective, but most gardeners will find the process of finding the ingredients and mixing up Bordeaux more work than they are willing to do to protect one or two backyard trees.  

Please see the Pest Note: Peach Leaf Curl for more information about this disease.