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 blisterlike growths or puckering of the leaves is common to all. The leaves are often thickened and almost crisp. Leaves turn downward and inward and may become red or purple. Peach leaf curl is with us again this year. Conditions in many parts of the state have been ideal for this disease.

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°F to 70°F). Infected trees may show early leaf drop, but generally the life of the tree is not threatened. Repeated yearly infection may weaken a tree and predispose it to other problems. Fruit growers are often concerned because these fungi reduce fruit quality.

We recommend that fruit growers apply a single dormant fungicide spray before bud break, and most commercial growers incorporate that into their spray programs. Landscape managers should focus on promoting tree health through pruning, watering, and fertilization. Fungicides are not usually recommended. At this point in the season, fungicides would be useless against this disease. A few persons have called and asked why their fungicide sprays were ineffective. In one case, liquid copper was used; in others, bordeaux mix was used. Both chemicals should work against this disease. The timing of the spray may be part of the problem. The chemical must be applied when buds are still dormant but close to bud break. It is possible that some of the chemical may have been washed off before the buds began to grow. A more likely scenario is that the chemical was not sprayed thoroughly enough or that it 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. The fungus overwinters in bud scales and in cracks and crevices of the bark, so thorough coverage is necessary.

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.