Hypoxylon Canker (Hypoxylon mammatum)

From: Ostry, Michael E.; Wilson, Louis F.; McNabb, Harold S., Jr.; Moore, Lincoln M. 1988. A guide to insect, disease, and animal pests of poplars. Agric. Handb. 677. Washington, DC: U.S. Department of Agriculture. 118 p.

Importance- Hypoxylon girdles and kills stems and branches. Small trees can be killed in as little as 2 to 4 years. Stain and decay fungi enter trees through cankers, weakening trees so that they break in wind.

Look For: Young cankers that are slightly sunken, yellowish-orange areas on the bark of stems and branches, often associated with various insect wounds. Blistered bark of older cankers with gray hyphal pegs with asexual spores (conidia) under the bark. Advanced cankers with sexual spores (ascospores) in raised gray-black structures resembling cushions on the cankered stem surface.
Young canker associated with insect gall.	Blistered bark of older canker.

Biology- The fungus overwinters on cankered trees. Dead trees remain an inoculum source for several years. Ascospores from 3-year-old or older cankers presumably infect trees through various kinds of wounds or breaks in the bark near branches.

Monitoring- Examine trees for canker. Harvest seriously affected stands early to minimize losses. Oviposition wounds made by several species of insects can be colonized by Hypoxylon, so trees that have many of these wounds should be considered at risk.
Fruit bodies on old canker.	Advance decay of affected stem.

Control:

• No direct control measures are known. However, branch cankers, if detected early, can be removed by pruning to prevent the fungus from growing into the main stem.
• Hypoxylon is primarily a pathogen of the aspens, although occasionally certain hybrid poplars are also infected. Poplars in the Section Leuce (white poplars) should not be planted where Hypoxylon is known to be a problem.
• Maintain well-stocked stands. Thin stands and open-grown trees are favored by insects that can cause wounds through which Hypoxylon can enter.

For Additional Information:

Anderson, R. L.; Anderson, G. W. 1979. Hypoxylon canker of aspen. For. Insect & Dis. Leafl. 6. Washington, DC: U.S. Department of Agriculture, Forest Service. 7 p.

Anderson, G. W.; Martin, M. P. 1981. Factors related to incidence of Hypoxylon cankers in aspen and survival of cankers trees. Forest Science. 27: 461-476.

Anderson, N. A.; Ostry, M. E.; Anderson, G. W. 1979. Insect wounds as infection sites for Hypoxylon mammatum on trembling aspen. Phytopathology. 69: 476-479.

Ostry, M. E.; Anderson, N.A. 1983. Infection of trembling aspen by Hypoxylon mammatum through cicada oviposition wounds. Phtopathology. 73: 1092-1096.

Schipper, A. L.; Anderson, R. L. 1976. How to identify Hypoxylon canker of aspen. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 6 p.