⚠ Moderate Urgency

Oozing Sap or Bleeding Cankers on Trees

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What It Means Causes Trees Affected How Urgent What To Do Call an Arborist?Regional Notes Related Pests FAQ

What This Symptom Usually Means

Oozing or bleeding from tree bark has several causes. Bacterial wetwood (slime flux) produces foul-smelling, dark ooze from wounds or branch stubs — it is unsightly but usually not fatal. Phytophthora bleeding cankers produce dark, water-soaked bark with reddish-brown ooze — this is more serious. Normal sap flow from pruning wounds or mechanical damage is clear to amber and is not a concern. Alcoholic flux produces frothy, fermented ooze that attracts insects — it occurs in heat-stressed trees.

Most Likely Causes

Bacterial wetwood (slime flux)

Dark, foul-smelling liquid oozes from wounds, cracks, or branch stubs. Caused by bacteria that ferment internal sap. Common in elms, oaks, maples, and poplars. Usually chronic but not fatal.

Phytophthora bleeding canker

Dark, reddish-brown ooze from the lower trunk bark. The bark underneath is water-soaked and discolored. Attacks the cambium and can girdle the tree. Serious on oaks, beeches, and horse chestnuts.

Normal sap flow

Clear to amber sap weeping from recent pruning cuts or wounds. Maples and birches bleed heavily from winter/spring pruning cuts. This is normal and stops on its own.

Alcoholic flux

White, frothy, fermented ooze with a beer-like smell, often attracting butterflies, beetles, and wasps. Occurs during heat stress. Usually resolves when temperatures moderate.

Canker diseases

Various fungi and bacteria cause sunken, oozing cankers on bark. The ooze may be clear, amber, or dark depending on the pathogen.

Trees Commonly Affected

Oak

Bacterial wetwood and Phytophthora are both common. Also susceptible to oak wilt sap staining.

Elm

Bacterial wetwood is extremely common in elms

Maple

Normal sap bleeding from pruning; also gets bacterial wetwood

Beech

Phytophthora bleeding canker is a significant threat

Horse Chestnut

Bleeding canker from Pseudomonas is a major problem in some regions

Birch

Bleeds heavily from spring pruning cuts — this is normal

How Urgent Is This?

⚠ Moderate Urgency

Moderate. Bacterial wetwood is chronic and mostly cosmetic. Phytophthora bleeding canker is more serious and can girdle the trunk over time. Normal sap flow from pruning requires no action. The key is distinguishing between benign bleeding and pathological oozing. If the bark around the oozing area is sunken, discolored, or the wood underneath is dark and water-soaked, it needs attention.

What You Can Do Right Now

Determine if the ooze is from a wound (normal sap), a crack or stub (likely wetwood), or intact bark (could be Phytophthora or canker).
Note the color and smell: foul-smelling dark liquid (bacterial wetwood), reddish-brown staining (Phytophthora), clear/amber (normal sap), frothy/beer-smell (alcoholic flux).
Do NOT drill holes to relieve pressure — this was once recommended but research shows it creates additional entry points for disease.
Improve drainage if the oozing is on the lower trunk and soil stays wet.
Keep the area clean but do not try to seal or cover the oozing site.
Reduce stress on the tree: water during drought, mulch the root zone, avoid soil compaction.

When to Call a Certified Arborist

Contact a certified arborist if any of these apply:

✓Dark ooze is coming from intact bark on the lower trunk (possible Phytophthora)
✓Cankers are expanding and you see sunken, dead bark around the oozing area
✓The oozing is associated with branch dieback or canopy decline
✓Multiple trees are affected simultaneously
✓The tree is near a high-traffic area and the ooze is attracting stinging insects

Find an Arborist Near You

State & Regional Differences

Midwest

Bacterial wetwood is extremely common in urban elms and oaks. It stains bark and sidewalks but is rarely fatal. Phytophthora is less common in well-drained soils.

Southeast

Phytophthora is a major issue in clay soils with poor drainage. Warm, wet conditions promote rapid canker expansion.

West

Phytophthora ramorum (sudden oak death) causes bleeding cankers on oaks and tanoaks in coastal California and Oregon.

Northeast

Beech bark disease creates entry wounds for various oozing infections. Bacterial wetwood is common in street trees.

Frequently Asked Questions

Is oozing sap a sign my tree is dying?

Not necessarily. Bacterial wetwood ooze, while unpleasant, is usually a chronic condition that trees live with for decades. Normal sap flow from pruning wounds is harmless. However, Phytophthora bleeding cankers and expanding fungal cankers can be life-threatening if they girdle the trunk. The key distinguishing factor is whether the bark around the oozing area is alive (usually okay) or dead and sunken (more concerning).

Should I seal the oozing area on my tree?

No. Do not apply wound sealant, paint, tar, or any covering over oozing areas. Sealing traps moisture and bacteria inside, potentially worsening the condition. Do not drill drainage holes — this creates additional wounds. The tree's best chance is to compartmentalize the infection naturally.