According to fruit pathology specialist Dr. Steve Ries, peach leaf curl is now at epidemic levels throughout most of Illinois. On every infected tree that Ries has seen, all of the leaves have been infected. Confirmations of the disease have come from local homegrowers in Champaign as well as from the CES educator in DeWitt County, Pat Toohill.

Peach leaf curl occurs on peach, nectarine, and some ornamental Prunus species. It also occurs, although rarely, on cherry and plum. Leaf distortion and blisterlike growths or puckering of the leaves is common. The leaves are often thickened and almost crisp; they turn downward and inward and may become red or purple.

The causal fungi (Taphrina) 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. 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 of reduced fruit quality. Ries said that peach trees showing leaf infection will also have infected fruit.

Why is the disease so prevalent this year? Ries suggests two reasons. First, the typical control for this disease on a peach tree is a dormant fungicide spray that cannot be applied after the tree breaks dormancy. The spray can be applied any time after fall leaf drop and before spring bud swell. Bud swell this year was a full three weeks earlier than usual, which may have caught many growers off guard, resulting in a missed application. The second reason for increased disease is likely the fact that peach buds took a long time to open due to cool temperatures after budbreak, which allowed the window of opportunity for fungal infection to be left open longer than usual.

The good news is that peach leaf curl is a monocyclic disease—&there is no secondary infection. The leaves will pucker and curl, spores will form on the leaves and fruit (peach fruit), and leaves will fall. Peach fruit will be shriveled and drop early. Then infected species will form new leaves that will not be infected. Growers and homeowners can help their trees by applying a 12-12-12 or similar fertilizer now. Do not overfertilize: Ries recommends no more than 2 to 3 pounds of 12-12-12 per tree. The idea is to help the tree produce new leaves and allow it to go into dormancy in late summer.

The heavy infection this year means inoculum levels will be high for next year. Peach growers should mark their calendars now to remind them to apply a dormant fungicide spray (Bravo, Carbamate, Ziram, Bordeaux, copper hydroxide, or copper oxychloride) in the first week of February 1998. Spraying now will do nothing to stop peach leaf curl or leaf blisters.

For more information on leaf curls and blisters, consult Report on Plant Diseases No. 805, Peach Leaf Curl and Plum Pockets, or No. 663, Oak Leaf Blister.