Peach leaf curl is a common disease of peach trees that, while not usually fatal, can weak a tree enough to cause death in severe cases. It is especially prevalent in moist, mild winter areas though colder parts of the country can have problems during unusually warm, wet springs. Peach leaf curl is caused by a fungus, Taphrina deformans, that overwinters in the bark and on the buds of peach and nectarine trees.
About Peach Leaf Curl
A tree infected by peach leaf curl will sprout normal leaves in early spring, but some of the leaves will soon develop puckered, twisted areas that become thickened and reddish purple in colour. They gradually become brittle, with a whitish powder on the surface, then turn brown and fall off the tree. In severe cases, shoots are stunted and yellowed and flowers abort or the fruit becomes reddish and bumpy and falls before ripening.
The fungus itself spreads by spores from affected leaves that sprout and cover the shoots during summer without damaging the tissue. In the fall, the organism washes into cracks in the bark and buds and in spring it develops the threadlike mycelium that causes the stunting and twisting of the leaves.
Before considering types of sprays, be sure that you do everything possible to check the disease culturally. If you live in an area where peach leaf curl is common, plant one of the resistant varieties available locally. If you have only a few affected leaves, remove them by hand and burn or place in the garbage can, not the compost. Since the fungus overwinters in cracks on the tree, raking up and destroying leaves in fall will not substantially affect the level of infection, but should be done anyway for general insect and disease control.
As with all disease control, be sure to get local advice from your extension service on the best spray to use in your area. The best spray is one they recommend. General peach leaf curl recommendations include copper sprays, chlorothalonil and ferbam. Be sure to buy one that is labelled for use on edible crops and follow all label instructions.
Apply this spray in fall, after leaves have mostly fallen off the tree, and be sure to use a sticker, something that helps the spray spread on stick on the waxy twigs. In mild, wet winter areas or if your tree was previously affected, apply also in spring before the buds break.
Caring For An Affected Tree
Pamper your affected tree with plenty of water and fertilise with a product containing nitrogen for leaf growth, but don't apply fertiliser after August 1st to allow the tree to harden off for winter. Thin excess fruit to avoid extra demands on the branches.