White Spots on Maple Trunks: Harmless Lichens vs. Fungal Leaf Loss

White Spots on Maple Trunks: Harmless Lichens vs. Fungal Leaf Loss

Gray-green, crusty spots on maple bark are lichens—symbiotic organisms that are harmless and indicate clean air. They do not cause leaf loss. Premature defoliation on one tree with spread to others suggests a foliar fungal disease (e.g., anthracnose, tar spot) favored by wet springs.

Action Plan

• Ignore lichens; they benefit the ecosystem.
• Rake and destroy all fallen leaves to reduce fungal spores.
• Apply a preventive fungicide (chlorothalonil) at bud break next spring if defoliation was severe.
• Fertilize with 10-10-10 at 1 lb per inch of trunk diameter to boost tree vigor.

Atomic Grow, an organic spray, can also enhance leaf health and disease resistance.