Green Growth on Fruitless Mulberry: Lichens Explained

If you've noticed a greenish, crusty or leafy growth on the limbs of your 30-year-old fruitless mulberry trees in the Dallas area, you're likely seeing lichens—not a harmful fungus.

What Are Lichens?

Lichens are fascinating symbiotic organisms composed of fungi living in partnership with algae or cyanobacteria. They're not parasites; they manufacture their own food through photosynthesis and simply use the tree's bark as a substrate. Three main growth forms exist: crustose (tightly pressed against the bark), foliose (leaf-like but closely attached), and fruticose (shrubby or hanging).

Why They Appear on Your Trees

Lichens thrive in areas with high humidity and clean air. They're most noticeable on trees with thin canopies that allow more light to reach the bark. Their presence often indicates the canopy has already thinned due to age, stress, or other factors—not that the lichens caused the decline.

Impact and Management

Lichens have only a slight negative effect on trees. The best "control" is improving tree vigor: proper watering, fertilization based on soil test results, and pruning to encourage a denser canopy that shades the bark. A healthy, full canopy naturally suppresses lichen growth by reducing light penetration.

For your mature mulberries, apply a balanced 10-10-10 fertilizer at 1 pound per inch of trunk diameter, scattered beneath the canopy and watered in well. Skip the baking soda treatments—they're unnecessary and impractical for large trees. Focus on overall tree health instead.