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Extension > Garden > Yard and Garden > Trees and shrubs > Eutypella Canker

Eutypella Canker

Rebecca Koetter and Michelle Grabowski

S. Schimek, MN Dept. of Agriculture

Figure 1. Young canker on a maple sapling.

Importance

Eutypella canker is common on maple trees (Acer spp.) in landscape plantings and in natural areas. Cankers often form on the main trunk or major branches of the tree. Small trees that are less than 4 inches in diameter are commonly killed when the canker girdles the main trunk. On older trees a perennial canker forms. This is a very slow growing disease that trees will battle for decades before decay turns the tree into a hazard that requires the tree to be removed.

Pathogen and susceptible plants

Eutypella canker is a fungal disease caused by Eutypella parasitica. All trees in the genus Acer are susceptible to this disease (Table 1) including all maples that grow in Minnesota, box elder and sycamore trees. No species, or cultivars of the genus Acer (maples) have resistance to Eutypella canker, but no other shade trees are commonly affected by the disease.

Table 1. Maples affected by Eutypella canker

Common name Scientific name
Black maple Acer nigrum
Box elder  Acer negundo
Norway maple Acer platanoides
Red maple Acer rubrum
Silver maple Acer saccharinum
Sugar maple Acer saccarum

M. Grabowski, UMN Extension

Figure 2. Large old canker on a mature maple.

Identification

Biology

M.Grabowski, UMN Extension

Figure 3. Cream colored fungal mycelia at the edge of the canker.

During rainy weather spores are ejected into the air from infected wood and can travel more than 75 feet on the wind. The fungus infects recently wounded or newly pruned small branches. Once in the tree, the fungus makes itself at home underneath the bark where it will penetrate into the wood and expand outward up to 1 inch per year. It kills the phloem (vascular cells that transport sugars from the leaves throughout the tree), the cambium (undeveloped cells that grow into new vascular cells) and can even invade and decay the sapwood of the tree. This decay can extend up to a foot into the tree and many trees infected with Eutypella canker break during strong storms and in high winds.

Each year during the growing season the tree will try to defend itself by creating a layer of wound wood around the edge of the canker. When the tree goes dormant for the season, the fungus breaks into this barrier and continues its progress. This back and forth growth can continue for decades. In very old cankers where the bark has finally sloughed off, rings of growth can be seen that reflect this annual battle between fungus and tree.

Management

M.Grabowski, UMN Extension

Figure 4. Black spore producing structures on the face of an old canker.

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