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Maple Trunk Growths Are Lichens, Not Disease

Fuzzy mustard-colored and gray-green patches on maple trunks in northern Ohio. Fungicide didn’t help.

Identification: Lichens

These are lichens—symbiotic organisms (fungus + alga), not pathogens. Common on older, declining, or shaded trees; also grow on rocks and fence posts. They do not harm the tree.

No Treatment Needed

Lichens indicate clean air and ample light. Focus on overall tree health (water, nutrients) rather than removing lichens.

Plant Diseases: Maple Gall Mites: Cosmetic, No Treatment Needed; Light Green Splotches on Gulf Coast Trees: Lichens, Not a Problem; Citrus Greasy Spot on Grapefruit: Copper Fungicide Timing; Red Maple Black Oozing: Phytophthora Bleeding Canker, Complex Management; Pine Green/Gray Fungus: Lichens, Not Disease; Lichens on Tree Trunks: Harmless but Indicative of Stress; Vinegar as Fungicide for Sarracenia: Experimental and Risky; Why Grass Fails Under Mature Maples and the Best Alternative: Mulch Rings; Maple Trees: Species Diversity, Uses, and Landscape Value; Maple Trunk Wound: Planting Too Deep, Mulch Volcano, Grass Competition

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