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Extension > Garden > Yard and Garden > Trees and Shrubs > Hypoxylon canker

Hypoxylon canker

Rebecca Koetter and Michelle Grabowski

Importance

In the Great Lakes region hypoxylon canker is the main cause of premature death to quaking aspen. It is one of the most destructive diseases to aspens in forest settings and can also be detrimental in residential landscapes. It is common for trees infected with hypoxylon canker to break in the wind.

M. Grabowski, UMN Extension

Figure 1. Brown leaves indicating a girdling canker.

M. Grabowski, UMN Extension

Figure 2. Hypoxylon canker showing peach colored margin and black and white center

Pathogen and susceptible plants

Entoleuca mammata (Syn. Hypoxylon mammatum) is the fungus that causes hypoxylon canker on aspen, poplar and willow (Table 1). The fungi also resides on but does not cause disease on several other shade trees including maple (Acer), oak (Quercus), elm (Ulmus), birch (Betula), alder (Alnus), Mt. ash (Sorbus), hornbeam or blue beech (Carpinus), apple (Malus), and pear (Pyrus).

Table 1. Trees affected by the disease in Minnesota.

Most susceptible Occasionally affected Rarely affected
Quaking aspen (Populus tremuloides) and hybrids Bigtooth aspen (P. grandidentata)

Balsam poplar (P. balsamifera)

European aspen (P. tremula) and hybrids

White poplar (P. alba) and hybrids Eastern Cottonwood (P. deltoides)

Violet willow (Salix daphnoides)
Black poplar hybrids (P. nigra)

Identification

M. Grabowski, UMN Extension

Figure 3. Fungal stromata pushing through bark on a canker older than 3yrs

Biology

The Hypoxylon canker fungus survives from year to year in cankers on infected trees. Gray to black cushion-like spore producing structures, that are 2-5 mm across, form crust-like patches on cankers that are 3 years or older. Spores produced on these structures are ejected through the air after rainy weather. If spores land on a susceptible host, infection will occur if air remains damp for up to 48 hours with temperatures above 60°F. Healthy bark is resistant to infection, but the fungus can infect through young dying twigs, branch unions with cracks or wounds made by insects. The fungus grows first through the wood, cambium and then into the bark, killing cells as it spreads into healthy tissue. The fungus continues to colonize the tree and usually within 3 to 8 years the tree is girdled and dies. Infected trees often break at the original point of infection due to wood decay under the canker.

M. Grabowski, UMN Extension

Figure 4. Fungal stromata turn completely black with age.

M. Grabowski, UMN Extension

Figure 5. Older cankers become riddled with holes from wood boring insects and woodpeckers.

Management


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