In contrast to oak wilt, which is lethal, this disease is relatively harmless. Still, it causes some concern because it can deform leaves and cause some leaf drop.

The disease is caused by a fungal species of Taphrina, and leaf distortion and blisterlike growths are common. The leaves are often thickened and almost crisp. The blistered areas turn from green to red to brown as the season progresses.

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 degree to 70 degree F).

Landscape managers should focus on promoting tree health through pruning, watering, and fertilization. Fungicides are not usually recommended for ornamental trees although they are useful on peaches for a related disease, peach leaf curls. If you are having problems with leaf curl and blisters and wish to use a fungicide control, mark your calendar for a late-fall or winter fungicide application.

Fungicide options for homeowners are listed in the Home, Yard, and Garden Pest Guide. Fungicides available to commercial growers are listed in the Commercial Landscape and Turfgrass Pest Management Handbook. For more on leaf curls and blisters, consult Report on Plant Disease, no. 805, “Peach Leaf Curl and Plum Pockets,” or no. 663, “Oak Leaf Blister. Both are available in Illinois Extension offices or on the U of I Web site (http://www.ag.uiuc.edu/%7Evista/horticul.htm).