Peach trees (Prunus persica) are desirable for their beautiful white, pink or red spring flowers and juicy, tasty fruit. This highly nutritious fruit has been cultivated for centuries in the United States. Peaches are second in popularity only to apples, according to Gary Gao of Ohio State University. Unfortunately, peach trees are somewhat susceptible to diseases.
Brown rot (Monilinia fructicola) is the most serious disease affecting peach trees, according to the University of Missouri. The fungus attacks the flowers, wood and fruit of the plant. It causes the flowers to turn brown, or manifests as a small brown spot on the ripening fruit that quickly spreads and causes the peach to rot and drop prematurely from the tree. On twigs and branches, it causes cankers, areas of cracked, infect wood that often ooze sap.
The only way to treat brown rot is to prevent it by applying a systematic fungicide in the spring. In addition, make sure your peach tree has plenty of room to grow, and never water young trees from above, as the fungus spreads on water.
Bacterial spot (Xanthomonas pruni) affects many kinds of fruit trees, but peaches are one of the most commonly affected. Small, irregular spots appear on the leaves and fruit of the tree, especially in varieties that develop late. The spots can range in color from rust to deep black. In time, the spots rot and drop out of the leaves, creating a ragged appearance in the foliage. In severely infected trees, premature leaf drop and subsequent defoliation can occur.
On the fruit, the disease manifests as small, sunken spots usually on the side facing the sun. The spots may merge, causing the skin of the peach to crack or burst open. Some fruit develops in a malformed manner. The only way to treat the disease is to prevent it from occurring. There are no completely effective chemical means to control it. The bacteria lives in cool, shady and moist soil, so plant resistant varieties (try Belle of Georgia, Candor or Harkin) in areas that have well-draining soil exposed to a lot of sunlight.
Peach-leaf curl is most serious when a cool, wet spring is preceded by a mild winter, according to Ohio State University Extension. The disease is caused by the fungus Taphrina deformans. While the fungus can attack all parts of the tree, it is usually first seen in the leaves. As the leaves open, they become deformed, thickened and reddish in color. In time, they become covered with the spores of the fungus, which turns them gray, and they drop from the tree. If flowers develop, which is rare, they are brown and will quickly drop. Infected twigs are stunted and slightly orange in color. Infected fruit, which is also rare, is covered with raised, bumpy spots.
Apply a lime sulfur or a copper-based fungicide over the entire tree in the spring. This will prevent the fungus, which can overwinter in the twigs of the tree, from spreading.