Forest Health > Insects and Diseases publication
Diseases of... Hardwood Stem
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OTHER STEM, BRANCH, AND TWIG CANKERS
See also:
Hypoxylon Cankers, and
Branch and Stem Cankers of Sycamore
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| Pathogens: |
Various fungi
Botryosphaeria spp.,
Botryodiplodia spp.,
Endothia spp.,
Diplodia spp.,
Dothiorella spp.,
Phomopsis spp. |
| Common Host: |
Hardwoods |
Significance: |
This miscellaneous group of diseases is caused by a wide variety of fungi acting alone or in combination, under a broad range of influencing circumstances. By and large, these diseases are not serious, but when trees are injured or weakened by environmental stresses, infections can cause significant damage. These diseases are generally a concern in urban or ornamental situations as opposed to commercial forest stands. Some cankers can be a problem however, in commercial forestry operations where hardwoods are intensively managed in plantations |
Recognition: |
Cankers, by definition, are flattened, sunken or depressed areas in the bark resulting from the death of the underlying cambium. Cankers often appear at dead branch stubs, the result of the progression of infections from smaller to larger branches. Cankers may be circular or somewhat target-shaped around old branch stubs, they may entirely girdle infected stems, or they may be narrow and elongated along one or more sides of infected stems. Cankered tissues often appear depressed as the surrounding live tissues tend to grow around the dead, cankered bark tissues. Pidges of folds of callus tissue are frequently present at the margins of cankered tissues. Terminal cankers (infections at the end of branches or twigs) commonly result in varying degrees of branch or crown dieback, accompanied by localized wilting or loss of foliage. Eventually, the canker-producing fungi produce small, dark or brightly colored (depending on the particular pathogen) pimple-like fruiting bodies on or embedded in the affected bark tissues. These structures are best seen with a hand lens, but may also be seen readily, in most cases, with the naked eye. Wood behind cankered bark tissues is usually discolored and often becomes decayed as a result of the ingress of wood decay fungi.
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Infection Biology: |
Spores of the various canker fungi are spread through the action of wind, rain insects, and possibly rodents and birds, as well as man. Infections occur at wounds, large and small, whenever the intact bark is broken, exposing the susceptible cambium tissues beneath. Other infections occur by direct penetration of the pathogens through intact bark tissues. This latter type of infection is particularly common where tissues are stressed by extreme temperatures or moisture deficiency. Spore production on infected tissues presumably occurs at any time of year when temperatures and moisture are adequate. |
Control: |
Control of stem and branch cankers is best achieved by prevention. Avoid injuries to trees and avert unnecessary stresses by providing adequate fertilizer and moisture to shade trees. Canker branches should be removed to reduce local fungus inoculum (spores) and prevent progression of the pathogen(s) into larger branches or stems. When removing cankered branches, make cuts well below the visible canker symptoms.
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Bulletin No. 196-A | Printed October, 1983 | Contact the Forest Health Section |
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