Both peach leaf curl and oak leaf blister are with us again this year. 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 to ornamental species. Still, repeated yearly infection may weaken a tree 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 of these diseases. Leaf distortion and blister-like growths or puckering of the leaves is common to all. The leaves are often thickened and almost crisp.
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 degreesF to 70 degreesF). Evidently, such weather did exist at the time of infection.
For fruit growers, we recommend a single dormant-fungicide spray applied in the fall after leaf drop or in the early spring before budbreak. This is common practice 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 through pruning, watering, and fertilization. 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 so you donít forget again.
Again this year a few have called and asked why their fungicide sprays did not control this disease. A likely scenario is that the chemical did not afford complete coverage. Hand sprayers often put out a rather coarse spray, and even coverage is difficult 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.
For more on leaf curls and blisters, consult RPD No. 805, Peach Leaf Curl and Plum Pockets, or No. 663, Oak Leaf Blister. Both are available on the Vista Web site listed previously.