Why Do Some Tennessee Trees Lose Bark or Develop Cankers?

Trees in Tennessee commonly show bark problems ranging from harmless natural shedding to serious cankers that threaten tree health and safety. Understanding why bark peels, cracks, or dies back into sunken lesions is the first step toward making good management decisions: protecting valuable shade trees, preventing spread of disease, and knowing when a professional is needed. This article explains the main causes, how to tell normal bark shedding from disease, practical diagnostic steps, treatment and prevention, and clear takeaways for homeowners and landscape managers in Tennessee.

Overview: bark loss and cankers — what the terms mean

A tree’s bark protects the living vascular tissue (cambium and phloem), moderates temperature, and provides structural defense against pests and pathogens. Visible bark loss or cankers can indicate:

normal exfoliation in species that naturally peel, or
localized lesions of dead bark and cambium (cankers) caused by injury, fungi, bacteria, insects, or environmental stress.

A canker is a dead, often sunken or cracked area on the trunk or branch where the cambium has been killed. Cankers are commonly the result of an organism entering through a wound or a zone weakened by stress.

Common causes of bark loss and cankers in Tennessee

Environmental and physiological causes

Sunscald and frost cracks

Winter sunscald occurs when warm daytime sun heats thin bark on the south or southwest side of the trunk, then rapid overnight cooling causes cell death. The result can be a flattened, dead patch of bark that later cracks and peels.
Frost cracks form when the trunk contracts rapidly in cold nights; vertical splits can allow pathogens to enter.

Drought and root stress

Prolonged drought, compacted soil, or root damage reduce a tree’s vigor. Stressed trees are more susceptible to opportunistic fungi such as Hypoxylon, Botryosphaeria, or other canker pathogens. In Tennessee’s hot summers and urban soils, drought stress is a frequent predisposing factor.

Natural exfoliation

Some species commonly found in Tennessee naturally shed bark without disease. River birch, American sycamore, and shagbark hickory have characteristic peeling or exfoliating bark that is normal. Knowing species traits prevents unnecessary treatment.

Pests and pathogens

Fungal cankers

Multiple fungi cause cankers on hardwoods. Hypoxylon is often associated with oak decline and appears on previously stressed oaks. Nectria and Botryosphaeria species cause perennial cankers on maples, beech, and other hosts. Fungal fruiting bodies, discoloration, and dead cambium under the bark are typical signs.

Bacterial cankers

Bacterial pathogens can produce sunken, water-soaked lesions that ooze sap or gum. Bacterial problems are common on fruit trees but also occur on some landscape species.

Insects and boring pests

Bark beetles, borers, and other wood-boring insects create entry wounds, gallery tunnels, and frass (sawdust-like material). Active boring often aggravates or initiates canker development, and insect galleries under the bark are diagnostic.

Mechanical injury and human causes

Lawn mowers, weed whackers, construction machinery, and even poorly positioned guy wires or stakes cause wounds. Wounds remove protective bark, giving pathogens direct access to the cambium.
Improper pruning (flush cuts that injure the branch collar) and “volcano” mulching that smothers roots and causes rot also increase vulnerability.

How to distinguish normal bark shedding from pathological cankers

Look for these visual clues:

Healthy exfoliating bark: regular, uniform peeling patterns consistent with species (e.g., river birch and sycamore patchy shedding; shagbark hickory long strips). Under the peeled layer you should see living cambium or pale, uninfected wood.
Pathological canker: localized sunken or cracked area, often darker than surrounding bark, sometimes with raised callus edges, oozing sap, fungal fruiting bodies or visible insect frass. When bark is removed, the cambium beneath a canker is brown, dry, and nonviable.
Multiple cankers, branch dieback, thinning crown, epicormic shoots (sprouts on trunk) and fungal fruiting bodies are signs of systemic decline rather than normal shedding.

Practical diagnostic steps for homeowners and property managers

Inspect the tree from all sides, noting location of damage (south or southwest side suggests sunscald; wounds near ground suggest lawn equipment).
Gently remove a small patch of loose bark at the edge of the lesion to expose the cambium. Healthy cambium is creamy-green; dead cambium is brown and dry.
Look for additional signs: frass (sawdust), insect holes, fungal fruiting bodies, oozing sap, and crown symptoms (dead branches, thinning).
Record the pattern and size of cankers and take clear photos. Serial monitoring over weeks shows whether cankers are expanding.
If diagnosis is uncertain or the tree is large/valueable, contact a certified arborist or extension agent for a professional assessment and possible tissue sampling.

Management and treatment options

Cultural and sanitation measures

Maintain tree vigor: deep watering during drought, proper mulching (2-4 inches of organic mulch, kept away from direct trunk contact), and avoiding soil compaction around the root zone.
Prevent mechanical wounds: keep mower and trimmer blades away from trunks, avoid piling soil or mulch against bark, and protect trunks during construction.
Sterilize pruning tools between cuts when working on diseased trees. A common field disinfectant is 70% isopropyl alcohol or a 10% bleach solution (rinse tools after bleach to prevent corrosion).

Correct pruning and removal of infected tissue

For active branch cankers, prune out infected branches back to healthy wood, making cuts several inches beyond the visible margin. Make clean cuts at the branch collar without leaving stubs.
For trunk cankers, if infection is limited and trees are otherwise vigorous, remove surrounding dead wood and monitor. If cankers girdle the trunk, the tree may not recover and removal is often necessary.
Proper disposal: burn, bury, or remove and dispose of infected wood away from the site. Do not chip heavily diseased material and leave it in contact with healthy trees.

Chemical controls and limitations

Fungicides and bactericides have limited effectiveness once a canker is established in the bark and cambium. Preventive sprays can protect pruning wounds in high-value trees or in nursery settings, but they are rarely a practical cure for field trees.
Insect control for borers may be appropriate if active insect infestation is detected; timing and product selection are species-specific and often best directed by an arborist or extension professional.

When removal is the appropriate option

Trees that are extensively girdled, unstable, or significantly declining despite treatment should be removed for safety. Dead or dying trees can attract insects and pose hazards in storms.

Prevention: best practices for Tennessee landscapes

Plant suitable species for site conditions, selecting trees adapted to local soils and climate.
Avoid planting too deep and maintain a healthy root zone with mulch (but not against the trunk).
Water deeply and infrequently, especially during the first few years and during summer droughts.
Prune correctly and at appropriate times (late winter or dormant season is often recommended for many hardwoods), and avoid unnecessary wounds.
Protect trunks from mechanical damage and avoid piling soil or mulch against bark.
Monitor trees seasonally so early problems are noticed and addressed quickly.
Replace highly susceptible species near high-risk sites with more resistant alternatives if repeated problems occur.

When to call a professional

When cankers are expanding despite home care, when large scaffold limbs are affected, or when the tree presents a safety hazard (leaning, cracked trunk, large dead limbs).
If you cannot identify the cause (fungal vs. insect vs. abiotic), a certified arborist or local extension service can provide diagnosis, lab testing, and a management plan.

Practical takeaways

Not all bark peeling is disease: identify the tree species and compare the pattern to natural exfoliation before reacting.
Many cankers follow wounds or stress: prevention through good tree care (watering, mulching, avoiding wounds) is the most effective strategy.
Early detection and local pruning of infected branches, coupled with sanitation, can slow disease spread. Once a canker girdles the trunk or the tree is in serious decline, removal is often the safest choice.
Use professional help for diagnosis and for large or hazardous trees; chemical controls are rarely a standalone cure for established cankers.

Understanding the specific cause of bark loss or cankers allows for targeted action: prevent avoidable injuries, maintain tree vigor, prune and sanitize correctly, and call an arborist when necessary. With timely management and good cultural practices, many Tennessee trees will recover or be safely replaced before they become hazards.