How to Identify Quaking Aspen Diseases

If any tree has a right to be a hypochondriac it is the quaking aspen (Populus tremuloides). This fast-growing small to medium sized tree is affected by a plethora of disease pathogens. In fact, Colorado State University Cooperative Extension agents claim that quaking aspen problems make up the bulk of calls to their offices about tree problems. A lot of the tree’s problems are attributed to its thin bark which is easily wounded. Hardy to USDA zone 3, despite their sickly ways, quaking aspens are popular for their brilliant gold fall foliage.

This is by no means an exhaustive rundown of what to expect from the various pathogens that attack the quaking aspen, but it will give you a start. If you have any doubts about what is ailing the tree, contact the county cooperative extension office in your area.

Aspen Heart Rot
Aspen heart rot (Phellinus tremulae) decays the tree from the inside out. Early symptoms take place within the tree while on the outside it appears healthy. As the disease progresses the tree loses its structural integrity and, according to foresters with the U.S. Department of Agriculture, diseased aspens are prone to windsnap and may blow over. In the home landscape this may be disastrous, so remove the tree at the earliest signs of weakness. This disease is primarily one of the mature quaking aspen, gaining access through wounds in the tree’s bark.

Cytospora Canker
The first symptoms of cytospora canker includes tiny black bumps on the quaking aspen’s bark. Later you may notice orange markings near a wound in the tree’s bark. Advanced symptoms include dead bark falling from the tree. As the fungus spreads into living tissue it causes girdling, cutting off nutrients and water. Avoid cytospora canker by keeping the quaking aspen tree healthy and avoiding wounds. Keep pests to a minimum as even small wounds they create give the fungus an opportunity to invade the tree.

White Trunk Rot
White trunk rot (Ganoderma applanatum) is evidenced by cankers — actually known as basidiospores — on the tree’s trunk. These are flat, shelf-like or hoof-like structures that are dark brown to black on the top and tan to white on the bottom. There may be a lot of hidden decay in the tree which could be dangerous in the home landscape. There is no control for white trunk rot and removal of the tree is your best course of action.

Shoestring Root Disease
Shoestring root disease (Armillaria) bothers many plants and the quaking aspen is particularly susceptible. The first symptom you may notice is a reduction in growth and yellow leaves. Later, clusters of cream to brown colored mushrooms grow on the trees in summer and fall. Shoestring root disease won’t kill the quaking aspen unless it is already in a weakened state.

Hypoxylon Canker
Caused by the fungus Hypoxylon mammatum, hypoxylon canker is a killer. Initial symptoms include cankers that appear as sunken yellow areas on the bark. Soon, the outer bark develops blisters and peels off. The inner bark is black. Mature cankers may be several feet long, according to scientists with the U.S. Forest Service. The disease causes a slow death, with many trees dying within five years. Unfortunately there is no control for hypoxylon canker.

Photo Courtesy: Scott Catron/Wikimedia Commons

For more information, please consult the following webites:
United States Department of Agriculture: Cytospora Canker of Quaking Aspen

University of Wisconsin: Tom Volk’s Fungus of the Month for February 2004

USDA Forest Service: How to Identify and Minimize White Trunk Rot of Aspen

British Columbia Ministry of Forests: Armillaria root disease, Armillaria Ostoyae

USDA Forest Service: Hypoxylon Canker of Aspen