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FS ShieldForest Health Protection, Southern Region


caused by Hypoxylon spp.

Importance. - Fungi in the genus Hypoxylon generally cause a white rot of hardwood slash. However, some species are known to cause severe cankering of stressed hardwoods. Cankering caused by this fungus contributes to the premature death of trees stressed by drought, construction damage, or other problems. Rapidly rotting tissue leads to structural weakening, which causes serious hazard to people or property in high-use areas.

Identifying the Fungus. - The fungus is usually visible as a definite fruiting layer that has dislodged the bark. Fruiting layers vary in color. Hundreds of small, black fruiting bodies are imbedded in this layer.

Identifying the Injury. - The fungus invades the tree's cambium, and the fruiting layer exerts sufficient pressure to dislodge the bark. Careful observation is sometimes needed to see the fruiting layer, since it can resemble the bark of some trees, such as hackberry.

Hypoxylon canker on oak

Hypoxylon canker on oak. (Click for detail. JPG 35K).

Biology. - Weakened trees are most often attacked by Hypoxylon spp. The fungal spores enter wounds, germinate, and grow into the cambium, severely cankering and often girdling the tree very quickly. Concurrently, white rot of the sapwood under the canker begins. Fruiting structures eventually cover the cankered area and rupture the bark. Spores are produced at a rapid rate and are wind borne to new hosts.

Control. - Disease prevention can be achieved in high value trees by keeping the tree vigorous and unwounded. Fertilize high value trees and water them during drought periods. Once infection has occurred, remove infected limbs or trees, because they rapidly become hazardous to people and property.