Lichens on Trees and Lilacs: Harmless and Manageable

What They Are

Symbiotic algae+fungi. Three forms: crustose (flat), foliose (leafy), fruticose (bushy). Common in high humidity.

Slight negative—indicate thin canopy, not cause. Epiphytes (air-fed), not parasites.

Best: Improve tree vigor → dense canopy shades limbs → reduces lichen photosynthesis.
Chemical: Copper fungicides (Kocide 101, Kocide DF) temporarily suppress. No registered pesticides.

Lichens are cosmetic indicators of thin canopy. Cultural improvement is the sustainable solution.

Trees: Diagnosing and Treating Browning Fraser Firs and Cedar Trees; Light Green Splotches on Gulf Coast Trees: Lichens, Not a Problem; Lichens on Trees: Harmless Indicators of Stress, Not Killers; Walnut Caterpillars Defoliating Pecans: Identification and Control; Oaks Falling with Internal Decay: Hazard Tree Assessment Needed; Cypress Trees Submerged in Pond: Likely Dead; Cottonless Cottonwood Sparse Foliage: First-Year Root Establishment; Mushrooms on Confined Urban Oaks: What Those Cold-Weather Fungi Mean; Sudden Oak Death and Ash Tree Decline in Ohio; Identifying Harmless Lichens on Tree Bark

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