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Peach, Plum, and Cherry Disease Fact Sheets

Includes anthracnose, bacterial canker, bacterial spot, black knot, brown rot, cherry leaf spot, crown gall, cystospora canker, peach leaf curl, plum leaf spot, plum pox, plum pockets, powdery mildew, rhizopus rot, peach scab, prunus stem pitting, and rusty spot.

The first report of anthracnose occurring in the United States came from California in 1916, where it was found on almond. Significant losses from peach anthracnose were prominent during the late 1940s, especially in the southeastern states. Most years, anthracnose is considered a minor disease of peach. In past years the disease has occurred sporadically on fruit. If left unchecked, peach anthracnose can cause serious fruit rot infection.

While bacterial canker can occur on all stone fruit trees, and on apple and pear blossoms, it is important only on sweet cherry and ornamental flowering cherry trees in the northeastern United States. It is caused by the bacterium Pseudomonas syringae. Several other names (most commonly, gummosis and sour sap) have been used for the same disease.

Bacterial spot occurs in most countries where stone fruits are grown. The disease is caused by a bacterium Xanthomonas arboricola pv. pruni (formerly Xanthomonas campestris pv. pruni).

Black knot of plum, caused by the fungus Dibotryon morbosum, is well-named because of the characteristic black, warty knots it forms on branches of infected trees. Such trees grow poorly and gradually become stunted; occasionally, their limbs may be girdled. The disease is most important on plum trees and, secondarily, on cherry trees.

Brown rot is caused by the fungus Monilinia fructicola. It affects peaches, apricots, nectarines, plums, and cherries. The disease can also infect apple fruit late in the season, especially if the orchard is in proximity to stone fruit with a high incidence of brown rot. It is one of the major stone fruit diseases in Pennsylvania.

Cherry leaf spot, caused by the fungus Blumeriella jaapii (formerly Coccomyces hiemali), attacks the leaves, leaf stems, fruit, and fruit stems of tart, sweet, and English Morello cherries.

Crown gall is caused by a bacterium, Agrobacterium tumefaciens, and affects peaches, nectarines, apricots, plums, cherries, apples, pears, and quince. Peach and Mazzard cherry rootstocks are especially susceptible. The disease is common in tree fruit nurseries and can occur in orchards.

Cytospora canker is one of the most destructive diseases of peaches, nectarines, apricots, sweet cherries, and plums in Pennsylvania. Also known as perennial canker, peach canker, Leucostoma canker, and Valsa canker, the disease may cause trees in young orchards to die. Infected trees in older orchards gradually lose productivity and slowly decline.

The peach leaf curl fungus, Taphrina deformans, destroys early peach leaves. Although new leaves develop, their growth reduces established food reserves, weakens the tree, and may reduce yield. Defoliation by peach leaf curl in successive seasons may kill the tree.

Peach scab is an important disease in warm, humid peach-producing areas of the world. The fungus can be extremely damaging to trees throughout the mid-Atlantic region because of the typically warm, wet weather during the day through the mid-season period. The disease appears to affect all cultivars of peach and is known to occur on nectarines and apricots as well.

Leaf spot of plums and prune-type plums is caused by the fungus Coccomyces prunophorae.

A number of diseases of stone fruit are caused by fungi similar to the leaf curl fungus. In the northeastern United States, the most important disease affecting American-type plums is known as plum pockets, or bladder plum. It is caused by Taphrina communis.

Plum pox virus (PPV), or Sharka, is a viral disease that infects not only plum but other economically important Prunus species, including peach, nectarine, apricot, almond, and cherry, and ornamentals, such as flowering almond and purple leaf plum.

The disease is caused by Podosphaeria oxyacanthae, one of the common species of the powdery mildew group of fungi.

Powdery mildew, sometimes called rose mildew (it affects some woody ornamentals), is not often serious. The causal fungus, Sphaerotheca pannosa, attacks leaves, twigs, and fruit.

Trees infected with tomato ringspot virus (ToRSV) have the general appearance of being girdled, and the leaves appear drought stressed, and the disease is referred to as peach, or prunus, stem pitting.

Rhizopus rot, caused by Rhizopus nigricans, can be very destructive to harvested fruit. While it can develop in hail-injured or cracked fruit on the tree, it most commonly affects fruit in storage, during transit, and at the marketplace. Peaches, nectarines, sweet cherries, and plums are most susceptible.

Minor issue in Pennsylvania and is caused by the same fungus as apple powdery mildew. Loring is a susceptible variety.