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Elm Trunk Lichens: Harmless Epiphytes Indicating Thin Canopy

What They Are

Silver/gray and green blotches = lichens (algae + fungus symbiosis). Epiphytes—get nutrients from air, not tree. Three forms: crustose (flat), foliose (leafy), fruticose (shrubby).

Impact

Slightly detrimental (shade bark, minor).
Main issue: indicate thin canopy (more light = more lichens).

Best Control: Thicken Canopy

Fertilize: 10-10-10 at 1 lb/inch trunk diameter, 2 ft out to drip line. Water in or before rain.
Repeat in fall.
Denser foliage shades bark, reduces lichen photosynthesis.

No Spray Needed

Chemical removal not recommended for living trees.

Plant Diseases: Black Walnut Fern-Like Growth: Harmless Lichens, Not a Disease; Blue-Gray Growth on Tree Trunks: Lichens—Harmless, Indicate Light, Not Cause of Fruit Tree Decline; Lichens on Oak Trees: Harmless Epiphytes or a Sign of Stress?; Greenish-White Scale on Oak: Lichens, Not a Disease; Maple Tree Lichens: Harmless Epiphytes Indicating Canopy Thinning; Nuttall/Shumard Oak Lichen: Not Harmful but Indicates Stress; Black Trunk on Live Oak: Natural Aging or Lichens?; Light Green Growth on Pineapple Guava Trunk: Likely Lichen; Lichens on Oak and Roof: Harmless Epiphytes; Gray Fungus on Large Trees: Lichens, Not a Disease

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