It seems odd that the same disease could affect two widely differing hosts; but it is true. Oak leaf blisters and peach leaf curls 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 to ornamental species. Oak damage is mostly aesthetic. Still, repeated yearly infection may weaken an oak and predispose it to other problems.
Peach leaf curl occurs on peach, nectarine, and some ornamental Prunus species. Leaf curl, or leaf blisters, refers to a similar group of diseases on oak and occasionally on poplar. Several Taphrina species (fungi) cause all these diseases. Leaf distortion and blisterlike growths or puckering of the leaves is common to all. The leaves are often thickened, almost crisp. It is not unusual to confuse this with chemical injury or even early season cold injury to new growth.
The fungi survive over winter in buds and twigs, infecting leaves and flowers in the cool, moist weather of early spring, from bud swell to bud opening (ideally, temperatures are 50° to 70°F).
For fruit growers, a single dormant-fungicide spray is recommended. Apply in the fall after leaf drop or in the early spring before budbreak. This practice is common for most commercial growers. 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 by pruning, watering, and fertilizing--practices that help the tree refoliate. New leaves will not be infected this season. 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 blisters, mark your calendar for a late-fall fungicide application.
For more information, see Report on Plant Disease, no. 805, “Peach Leaf Curl and Plum Pockets,” or no. 663, “Oak Leaf Blister,” on Extension’s VISTA Web site; both include photos.