Peach leaf curl occurs on edible peach, nectarines, and some ornamental Prunus species. We sometimes see it on ornamental plums or ornamental peach. Leaf curl or leaf blister refers to a similar group of diseases on oak and occasionally on poplar. Several Taphrina species (fungi) cause all of these diseases. Leaf distortion and blisterlike growths or puckering of the leaves is common to all. The leaves are often thickened and almost crisp.
If your trees have had problems in the past and you did not spray a dormant fungicide this winter, you are most likely experiencing the problem again. These fungal diseases are caused by different species of Taphrina, a fungus that causes distorted, thickened leaves and early leaf drop. Leaves turn downward and inward and may become red or purple. The disease may cause yield loss in edible peach but is not seriously harmful on its own to ornamental species. Still, repeated yearly infection may weaken a tree and predispose it to other problems.
The causal fungi survive over winter in buds and twigs. They infect leaves and flowers in the cool, moist weather of early spring, from bud swell to bud opening (ideally temperatures are 50 to 70°F). Here is another example of a disease that thrives in the cool, wet weather experienced this spring.
Fruit growers can easily control this disease with a single dormant fungicide spray applied in the fall after leaf drop or in the early spring before bud break. This is common practice for most commercial growers. A dormant fungicide spray is not the same as a dormant oil spray. Home fruit growers in Illinois who use a dormant fungicide and are careful to provide full coverage of buds do not have problems with leaf curl. Landscape managers should focus on promoting tree health through pruning, watering, and fertilizing. Fungicides are not usually recommended for ornamental trees. In all cases, fungicides would be useless against this disease now. If you are having problems with curl and blister, mark your calendar for a late fall or winter fungicide application so you don't forget again.
If you have used a dormant fungicide spray and did not control this disease, check these possibilities. Did you spray thoroughly enough to get complete coverage of the stems and buds? Hand sprayers often put out a rather coarse spray, and even coverage is dif-ficult to attain. It might be wise to put a spreader--sticker in with the spray and to spray until the tree glistens from the spray. The fungus overwinters in bud scales and cracks and crevices of the bark, so thorough coverage is necessary. Did you use the right chemical? Was the timing correct? Chemicals must be applied in the dormant season, either in late fall or early spring before buds swell. Fungicides for home-owners are listed in the Home, Yard, and Garden Pest Guide. Fungicides available to commercial growers are listed in the Commercial Landscape & Turfgrass Pest Management Handbook. For more on peach leaf curl of edible fruit, read the Illinois Fruit and Vegetable Newsletter, available on line at http://www. aces.uiuc.edu/ipm/news/fvnews.html.
For more on leaf curls and blisters, consult Report on Plant Disease (RPD) no. 805, "Peach Leaf Curl and Plum Pockets," or no. 663, "Oak Leaf Blister." Both are available in Illinois Extension offices or on the University of Illinois Extension Vista Web site.