Cause Fumago vagans, a nonpathogenic fungus that grows on the honeydew (excrement) of scale insects has been reported from the PNW. Several other fungi have been reported from southern states including Capnodium elongatum, Echidnodella angustiformis and E. prinoides. Sooty mold typically causes little damage to plants aside from an aesthetic problem. Very heavy fungal coverings on leaves may interfere with photosynthesis and cause some plant decline.
Symptoms A dark-green-to-black layer on the upper leaf surface. Black fungal growth may cover anything that the excrement falls on including other plants and even the walls or windows of an adjacent house.
Cultural control
- Wipe off leaves if black fungal growth is on only a few branches.
- Control scale insects. See the latest edition of the PNW Insect Management Handbook for current recommendations.
- Wash honeydew from plants with a strong stream of water. Choose a time when leaves will dry quickly.
Reference Hughes, S.J. 1976. Sooty moulds. Mycologia 68:693-820.