Black mold on cedars - Ask Extension
We moved onto some acres in southwestern Oregon back in November 2023. I've noticed small sections of cedars, mainly younger ones, getting covered in ...
Knowledgebase
Black mold on cedars #867828
Asked May 09, 2024, 10:41 PM EDT
We moved onto some acres in southwestern Oregon back in November 2023. I've noticed small sections of cedars, mainly younger ones, getting covered in a black mold. Is there anything I can do to help them, or should I let the forrest do its own work??
Josephine County Oregon
Expert Response
I can't be 100% certain without examining the tree over the season, but this looks a lot like sooty mold (the black) which is commonly reported on incense cedar due to a scale insect (Monterey Cypress Scale, Xylococculus macrocarpae (Homoptera: Margarodidae)). The insect is a sap sucking insect which expels honey dew. The honey dew drips onto the trunk and the mold grows on the honey dew.
Control therefore has to do with controlling the scale insect. However, the insect can be very difficult to control without insecticides, and even then it is tricky because scale insects are only vulnerable to insecticides at certain times of the year. You would want to confirm the scale insect is present before using any insecticides.
In general, it seems like the scale does not really cause that much damage and the mold is not doing anything to the tree, it just grows on the surface due to the honey dew. So I would not really worry about it.
Control therefore has to do with controlling the scale insect. However, the insect can be very difficult to control without insecticides, and even then it is tricky because scale insects are only vulnerable to insecticides at certain times of the year. You would want to confirm the scale insect is present before using any insecticides.
In general, it seems like the scale does not really cause that much damage and the mold is not doing anything to the tree, it just grows on the surface due to the honey dew. So I would not really worry about it.
