Taphrina leaf curl—Taphrina spp.
Taphrina spp. affect many different tree species. For example, the oak leaf blister fungus, Taphrina caerulescens =T. coerulescens, infects oaks and California buckeye. Peach leaf curl caused by Taphrina deformans affects the blossoms, fruit, leaves, and shoots of peaches, ornamental flowering peaches, and nectarines.
Leaves on infected trees become galled, curled, and may drop prematurely. Bulges may appear on upper leaf surfaces. Other factors can cause similar symptoms.
On oaks, blisters caused by Taphrina fungi may look similar to those caused by the live oak erineum mite, Eriophyes mackiei. Mites cause blistered leaves or galled twigs and occur in yellow to orange felty masses in depressions on the underside of blistered leaves. No felty masses of mites are found on the undersides of leaves infected with Taphrina spp. However, Taphrina produce masses of pale spores on leaf surfaces that resemble the felty mass caused by erineum mites. Taphrina spores (asci) can occur on either leaf surface; the felty colonies of erineum mites usually occur only on the underside of oak leaves.
Microscopic examination may be required to distinguish confidently between erineum mites and Taphrina spores. The minute eriophyid mites are about 1/50 inch long, about one-fourth the size of spider mites, and a 15 to 20× hand lens or preferably a binocular dissecting microscope is needed to distinguish them and determine whether eriophyid mites are present.
The fungi overwinter as spores (ascospores and conidia) in bark cracks and under bud scales. In the spring, young, germinating spores infect expanding leaves primarily through stomata (natural openings in leaves).
Infected tissue develops blisters, which are initially light green, yellowish, or whitish on the upper leaf surface and yellow-brown to gray on the underside of the leaf. As blisters age, their upper surfaces may turn reddish or purplish and then brown.
Disease is promoted by wet foliage during leaf flush. Usually only one disease cycle occurs per year.
Provide trees with proper cultural care to keep them vigorous. On oaks no other control is generally recommended. See Pest Notes: Peach Leaf Curl for management on Prunus spp.