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Disease Descriptions and Management

Bacterial spot occurs in most countries where stone fruits are grown. Common hosts include peach, nectarine, prune, plum, and apricot. Other hosts are sweet and tart cherry, almond, and wild peach.

Black knot of plum, caused by the fungus Apiosporina mobosa, is well-named because of the characteristic black, warty knots it forms on the branches of infected trees. Infected trees grow poorly and gradually become stunted; occasionally, their limbs are girdled. The disease is most important on plum, prune, and sour and wild cherry trees.

Brown rot, caused by the fungus Monilinia fructicola, is one of the major stone fruit diseases in Pennsylvania. The disease affects peaches, apricots, nectarines, plums, cherries, and most commercially grown Prunus species. The fungus can cause a blossom and twig blight, a canker, a leaf infection, and a fruit rot. Infected fruit will rot on the tree and after being harvested.

Cherry leaf spot, caused by the fungus Blumeriella jaapii, 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 peach, nectarine, apricot, plum, cherry, apple, pear, and quince trees. 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, Valsa canker, and Leucostoma canker, the disease can cause trees in young orchards to die. Infected trees in older orchards gradually lose productivity and slowly decline.

Peach leaf curl, caused by the fungus Taphrina deformans, is a common disease of peach and nectarine. This fungus destroys young peach leaves. Although new leaves develop, their growth reduces established food reserves, weakens the tree, and can reduce yield. Defoliation by peach leaf curl in successive seasons can kill the tree.

Leaf spot of plums and prune-type plums is caused by the fungus Coccomyces prunophorae. The fungus, its life cycle, and the disease it causes are very similar to those of cherry leaf spot.

A number of stone fruit diseases 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.

This disease is caused by Podosphaera clandestina, one of the common species of the powdery mildew group of fungi. The same fungus reportedly causes powdery mildew in peaches, apricots, apples, pears, quinces, persimmons, and a few ornamental plants.

Powdery mildew, sometimes called "rose mildew" (it affects some woody ornamentals), is often not serious. The causal fungus, Sphaerotheca pannosa, and rusty spot, a disease associated with mildew fungi, usually are rare in peach orchards. The fungus can attack leaves, twigs, and fruit.

Rhizopus rot, caused by Rhizopus stolonifer, can be very destructive to harvested fruit. Although 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.

The following general cultural controls will help to keep your trees healthy.

Peach anthracnose, often called ripe rot, is usually rare and considered a minor disease of peaches.

Bacterial canker of stone fruit is caused by the two related bacterial species, Pseudomonas syringae and P. morsprunorum.

Peach scab is an important disease of peach and nectarines and can be extremely damaging in warm, humid areas especially in the southeastern United States. The disease appears to affect all cultivars of peach and is known to occur on nectarines, plums and apricots as well.

Prunus stem pitting is an important disease of all stone fruits. It is also called prune brownline and constriction disease. Apple union necrosis and decline is caused by the same virus and nematode vector as is Prunus stem pitting.

Rusty spot of peach is characterized by the presence of rust-colored spots that can cover the entire surface of the fruit.