Tag Archives: Tree Bark

Tree Diseases on Bark

Canker disease swelling and girdling tree trunk

Prevent diseases on your tree’s bark from killing it. Knowing what type of disease is growing on or in your tree will help you take appropriate measures to treat it.

72tree.com gathered information on diseases that affect or appear on tree bark, how severe they are, and what actions are needed to prevent the disease from spreading.

Tree Bark Diseases

Tree bark completely covers a tree’s trunk, branches, stems, and twigs. It could be seen as a protective skin that repels insect infestations, shields against pathogens, and resists physical damage. Frequently, however, a stressed tree will likely develop one of the following:

Cankers on Trees

Cankers are dead areas of bark on a tree’s trunk or branch. Multiple factors can cause bark death, like damage caused by an impact, bacteria, or fungi. Pathogens such as bacteria or fungi are usually unable to penetrate healthy bark, but if the tree is stressed or the bark is damaged, infection is more likely. Consider the following types of cankers:

Wound Canker – These cankers, sometimes referred to as annual cankers, are most common at or near the base of a tree. They are typically caused by a lawnmower, vehicle, and/or maintenance equipment strikes or repeated abrasion.

Cankers resulting from impact wounds are severe threats that need to be prevented. Allowing conditions for these wounds to persist can result in the girdling and death of the tree.

Prevention: Create a safety zone using organic mulch or gravel around the tree.

Tip: Existing wounds should be carefully trimmed (without widening or deepening the wound), so the tree can properly seal the wound. Point out these wounds/repairs to your tree professional.

Perennial Canker or Cytospora Canker (Target-Shaped) – This canker is one of the more common diseases of shade and fruit trees. It is caused by one of several Cytospora fungi (Nectria, Strumella, Eutypella, etc.) and attacks multiple hosts, including:

• Apple (Malus domestica)
• Apricot (Prunus armeniaca)
• Ash (Fraxinus)
• Aspen (Populus tremuloides)
• Birch (Betula)
• Beeches (Fagus)
• Cherry (Prunus avium)
• Elm (Ulmus)
• Hickories (Carya)
• Maples (Acer)
• Peach (Prunus persica)
• Poplars (Populus)
• Walnuts (Juglans)
• Willow (Salix)

Cytospora infections can occur via bark wounds, at junctions of dead and live branches, or at poorly cut pruning wounds. The fungi slowly grow through bark during the tree’s dormancy (late fall and winter). Then, in the growing season, the host trees respond by compartmentalizing the affected areas. This alternating growth of the fungus and the tree forms a distinct elongated, target-like appearance.

Identification: These cankers will appear sunken on branches or trunks and present the following:

• Colors vary from off-brown to gray shades
• Black fungal structures (pycnidia) embedded in small bumps around the wound
• Brownish to orangish masses of spores being extruded from pycnidia
• Oozing sap and/or a wet appearance

Tip: These cankers slowly expand over time and can eventually girdle the branch or the whole tree (when located on the trunk). Ask a professional tree service to evaluate your tree and recommend a course of action.

Diffuse Canker – With these highly lethal cankers, necrosis spreads so quickly that the host can’t compartmentalize the area fast enough to stop its progression. The differences between these and other cankers are:

Necrotic diffuse canker on tree trunk killing bark

• No callus rings are formed, the affected area appears dark, sunken, and often moist
• Diffuse cankers continue expanding during the growing season
• When these cankers occur on a tree’s trunk, the tree will likely die

Some of the pathogens responsible for diffuse cankers are:

• Phytophthora dieback
• Cytospora canker
• Botryosphaeria canker
• Hypoxylon canker
• Chestnut blight

Identification: Diffuse cankers appear as sunken, dark areas similar to other cankers, but with no callus rings. It is common to see sap oozing from these cankers.

Note: Diffuse cankers move fast enough to completely girdle and kill their hosts in a single growing season.

Managing Pathogen-Driven Canker Diseases – As with nearly all tree problems, prevention is easier and less costly than treatment. Consider the following:

• Properly prune your tree (only in dry weather)
• Sanitize all pruning equipment with 10% bleach or 70% alcohol before and after each tree
• Remove and destroy any dead or infected material
• Prevent tree wounds (mechanical and environmental)
• Soil should be well-drained
• Improve tree health (water, fertilize, prune, and mulch)
• Apply a preventative chemical treatment to un-infected trees

Tip: Have your trees inspected annually by a professional tree service. Besides early detection of disease, you may identify other stressors that increase your tree’s susceptibility to developing cankers.

Mushrooms on Tree Bark

When you see mushrooms growing on a tree, be concerned. Mushrooms are the fruiting structures of fungi. For them to appear, the fungi must be well-developed and have caused extensive decay within the tree. Consider the following:

Mushrooms on a Tree Branch – Carefully prune the branch from the tree and destroy (burn) it. Avoid spreading pathogens from one tree to the next by sanitizing your equipment with 10% bleach or 70% alcohol before and after working on infected trees.

After removing all visibly affected limbs or branches, monitor your tree over the next growing season and have it thoroughly inspected for any other potential issues (decay-causing fungi can quickly spread throughout a tree).

Mushrooms on a Tree Trunk – Call a professional tree service as quickly as possible. Your tree’s trunk is likely suffering from extensive internal decay and needs removal.

Mushrooms growing through birch tree bark signaling internal decay

Mushrooms on a Tree’s Root Flare – Again, this is an urgent scenario. When mushrooms grow from the root flare, there is likely significant decay within the tree’s roots, potentially destabilizing the tree when winds and storms come through. The tree will likely require emergency removal.

Treatment: When dealing with mushrooms on your tree, you will be limited to removing affected limbs and branches. For this, prevention is easier and less costly than treatment. Consider the following:

• Properly prune your tree (3 cut method)
• Sanitize all pruning equipment with 10% bleach or 70% alcohol before and after each tree
• Remove and destroy (burn) any dead or infected material
• Prevent mechanical tree wounds
• Prepare your trees for severe weather events
• Soil should be well-drained to avoid root rot
• Improve tree health (water, fertilize, prune, and mulch)
• Apply a preventative chemical treatment to un-infected trees

Tip: Avoid disturbing these mushrooms. Trying to remove them can release billions of microscopic spores into the air, potentially spreading the disease to other trees, shrubs, and plants.

Tree Diseases

In this article, you discovered information about the diseases that affect and appear on tree bark, the damage they cause, and how to prevent them.

By taking swift action to treat or remove a diseased tree, you are protecting your property and surrounding trees.

When you ignore diseases appearing on tree bark, you risk the sudden death or destabilization of the tree and the expensive damages it can cause when it falls.

Sources:
uaex.edu/environment-nature/forestry/health/treecankers.pdf
extension.usu.edu/pests/ipm/notes_ag/fruit-cytospora
extension.colostate.edu/topic-areas/yard-garden/cytospora-canker-2-937/