Mold problems when harvesting a tree that has been on the ground too long

Jun 21

Written By Robert Guy

Common Mold & Fungal Growth in Downed Oak Wood:

1. White Rot

Appearance: White, stringy or fibrous areas inside the wood
Cause: Fungus that breaks down lignin, leaving behind light-colored cellulose
Effect: Weakens structural integrity; often found in oak left damp on the ground

2. Brown Rot (Dry Rot)

Appearance: Brown, crumbly, cube-like cracking patterns in the wood
Cause: Fungi that digest cellulose, leaving brittle lignin
Effect: Common in dead hardwoods; serious decay

3. Blue Stain Mold (Sapstain)

Appearance: Gray-blue or blackish streaks
Cause: Non-structural fungi that enter through wounds or cuts
Effect: Affects appearance but not strength; not toxic but undesirable for cooking

4. Black Mold (Aspergillus or Cladosporium)

Appearance: Black powdery or spotted surface mold, often on bark or damp ends
Cause: High moisture and limited airflow
Effect: Potential allergen; may be unsafe to burn for food use

5. Mycelial Mats (Fruiting Bodies)

Appearance: White or tan fuzzy growth; sometimes mushrooms or brackets
Cause: Indicates active fungal colonization
Effect: Clear sign the wood has been decomposing for too long

⚠️ Implications for Firewood Use

If you're cutting firewood from a post oak tree that’s been down more than 6–12 months, especially in humid conditions, it’s at high risk for internal fungal decay and mold. This kind of wood:

May not burn well (low heat output)
Could emit bad odors or excessive smoke
Is not suitable for cooking—especially if mold is present

✅ What to Do

Split the wood and inspect the inside: look for staining, softness, or odor
Avoid moldy pieces for cooking; if used for heat, burn only outdoors with good ventilation
Discard soft, punky, or visibly moldy logs—they've already begun decomposing