Cause Fumago vagans, a nonpathogenic fungus that grows on the honeydew (excrement) of scale insects.
Symptoms A dark-green-to-black layer on the upper leaf surface.
- Wipe off leaves if mold is on only a few branches.
- Control scale insects. See the latest edition of the PNW Insect Management Handbook for current recommendations.
Reference Hughes, S.J. 1976. Sooty moulds. Mycologia 68:693-820.