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Significance

Leucostoma canker of stone fruits is most severe on cultivated crops in orchards and ornamental plantings. It is a minor problem on Prunus species found in natural ecosystems. A related fungus species, Leucocytospora kunzei, causes Leucostoma canker (or Valsa canker) of ornamental blue spruce (Picea pungens), Norway spruce (Picea abies), Engelmann spruce (Picea engelmannii), and Douglas-fir (Pseudotsuga menziesii).

Leucostoma canker, also called perennial canker, Cytospora canker, and Valsa canker, is an important disease of peaches, nectarines, and sweet cherries in areas with cold winters, including Canada and the northern fruit-growing regions of the United States. Leucostoma canker also is associated with the complex set of factors that result in the peach tree short life syndrome in the southeastern United States, and is important on other stone fruits including prune and plum in California and Idaho. In Europe, the disease is important on apricot, peach, sweet cherry, and is part of the disease complex of stone fruits called 'apoplexy'. Leucostoma canker also occurs in South America and Japan.

Leucostoma persoonii has been reported on Prunus, Cydonia (quince), Malus (apple, crabapple), Pyrus (pear), Sorbus (mountain ash), and Populus (poplar and aspen). L. cinctum has been reported on Crataegus (hawthorn), Prunus, Malus, and Robinia (locust). However, the disease is most commonly found on cultivated peaches, nectarines, plums, and cherries. The first observations of peach tree cankers caused by Leucostoma spp. were made in 1900 in western New York, and a few years later in Missouri. The disease was reported in southern Ontario in 1912. Leucostoma canker reduces the bearing surface of productive trees, shortens tree longevity, and significantly increases labor costs related to disease management.

Young, infected twigs may die during the first year of infection. Larger branches often take several years to display severe damage. Infected trees decline and become more symptomatic with each growing season. Infections often result in the general deterioration and death of the host. The stress placed on the tree may also make it susceptible to infections by other pathogens.

Economic losses accumulate as cankered limbs die or break from the stress of carrying a normal crop of fruit. The portions of a branch distal to a canker may become less productive, and cankers enlarge to girdle a branch and kill it. Trees with multiple infections show markedly reduced productivity. Because peach trees are pruned to support 3 to 4 main scaffold limbs, loss of one or two of these main limbs to Leucostoma canker represents 25 to 50% loss of fruit production.

It is very difficult to manage this disease once it is well established. Regular monitoring of susceptible plants, proper pruning and effective surgery should be a priority for all commercial growers and home gardeners.

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