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Maple Trunk White Spots: Harmless Lichens

Large maples in Ottawa with white round spots (2–6 inches) on trunk up to crown, healthy canopy: lichens (fungi + algae symbiosis). Harmless, non-parasitic, indicate clean air and slow bark growth.

No Action Needed

Lichens cause zero damage.
Common on mature trees in wooded lots.
Enjoy as sign of healthy environment.

Do not scrape, spray, or treat. They are benign.

Plant Diseases: Identifying Lichen vs. Disease on Maple Trunks and Managing Frost Cracks; Black Spots on Japanese Maple Bark: Likely Harmless Lichens; Black Spots on Maple Leaves: Tar Spot Fungus—Rake Leaves, Reduce Inoculum, Tree Usually Fine; Japanese Maple Leaf Scorch and Color Change: Environmental, Not Disease; White Powdery Spots on Maple Leaf Undersides: Likely Insects; Maple Leaf Warts and Holes: Phyllosticta Leaf Spot; White Spots on Red Maple: Superficial Fungus/Algae, Not Harmful; Beech Blight Aphids on Large Maple: Systemic Soil Treatment; Maple Tree White Spots and Leaf Eaters: Lichen and Insect Control; Maple Leaf Galls: Harmless Cosmetic Issue

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