Black Trunk Coating on Mulberry Trees: Sooty Mold

A black, non-slimy, non-powdery coating advancing slowly on mulberry trunks and branches—while leaves remain large and green—is classic sooty mold. This fungus grows on honeydew, the sugary excrement of sap-feeding insects like aphids, scale, or whiteflies.

What to Do

1. Identify the insect. Inspect leaves and stems for small, immobile bumps (scale) or clusters of tiny insects (aphids).
2. Control the insects. For large trees, soil-applied systemic insecticides (e.g., imidacloprid) are practical. For smaller trees, horticultural oil or insecticidal soap can work if coverage is thorough.
3. Sooty mold will fade once honeydew production stops. No direct fungicide needed.
4. Maintain vigor. Water and fertilize appropriately to help the tree tolerate the infestation.

See the University of Arkansas fact sheet FSA-7555 for detailed sooty mold management.