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University of Minnesota Extension

Hypoxylon canker

Quick facts

  • Hypoxylon canker infects the trunk and branches of aspen and poplars.
  • Cankers on the main trunk can kill the tree in 3-8 years.
  • In the Great Lakes region hypoxylon canker is the main cause of early death to quaking aspen.
  • It is one of the most destructive diseases to aspens in forests and in the home landscape.
  • To manage this disease, prune out dead or dying branches before the infection reaches that main trunk.
  • Remove weak trees that have cankers on the main trunk. These trees often break in the wind.
Brown leaves due to a canker
Hypoxylon canker with peach edge
Stromata turn black with age
Older canker with insect and woodpecker holes

How to identify Hypoxylon canker

Leaf symptoms

  • Leaves on infected branches are small.
  • As the infection progresses, leaves turn yellow then brown.
  • Dead leaves often remain attached.

Branch and trunk symptoms

  • Cankers are infections of the bark and sapwood on branches or trunks.
  • Hypoxylon cankers have discolored bark and are round-to-oblong in shape. The edges of the cankers are irregular and wavy.
  • Cankers often form at branch unions, stubs, wounds or galls.
  • Young cankers have smooth, yellow-orange to orangish-brown bark compared to healthy, young, green-grey bark.
  • Old cankers have yellow-orange edges. The centers of old cankers develop a blotchy, salt and pepper appearance as bark blisters and peels away in small patches.
  • Small, gray pegs can be seen under blistered bark in cankers that are 2 years or older.
  • Clusters of small (2-5 mm across), gray-to-black bumps form on the exposed wood of cankers that are 3 years or older. These cushion-like structures produce fungal spores.
  • Wood beneath old cankers is often decayed and contains wood-boring insects.

Trees affected by Hypoxylon canker in Minnesota

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

Trees most likely to be affected

  • Quaking aspen (Populus tremuloides) and hybrids.

Trees occasionally affected

  • Bigtooth aspen (P. grandidentata)
  • European aspen (P. tremula) and hybrids
  • White poplar (P. alba) and hybrids
  • Violet willow (Salix daphnoides)
  • Black poplar hybrids (P. nigra)

Trees rarely affected

  • Balsam poplar (P. balsamifera)
  • Eastern Cottonwood (P. deltoides)

How does Hypoxylon canker survive and spread?

Older canker with stromata forming
  • Hypoxylon canker is caused by the fungus Entoleuca mammata (Syn. Hypoxylon mammatum).
  • This fungus survives from year to year in cankers on infected trees.
  • Stromata (gray-to-black, spore producing structures) form on cankers that are 3 years or older.
  • Spores are released into the air after rainy weather.
  • If spores land on a susceptible tree, infection will occur if air stays damp for up to 48 hours with temperatures above 60 F.
  • Healthy bark is resistant to infection. The fungus can infect a tree through young dying twigs, cracks at branch unions or wounds made by insects.
  • The fungus grows first through the wood and then into the bark. It kills cells as it spreads into healthy tissue.
  • The fungus continues to colonize the tree. Usually, the tree is girdled and dies within 3 to 8 years.
  • Infected trees often break at the original point of infection because of wood decay caused by the canker.

How to manage Hypoxylon canker

  • There are no fungicides that prevent or cure Hypoxylon canker.
  • Avoid planting aspen, poplar, and willow near trees with existing Hypoxylon infections.
  • Prune out dead or dying branches before the canker reaches the main trunk. Prune only during dry periods.
  • Remove structurally weak trees that have cankers along the main trunk. These trees can break and cause damage to people and property.

Rebecca Koetter and Michelle Grabowski, Extension educator

Reviewed in 2019

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