Sooty mold is a fungal disease caused by sap-sucking insects
Sooty mold is a fungus that is dark-colored and grows on the honeydew produced by sap-sucking insects like aphids. This fungus appears as a black, powdery substance that can cover leaves and twigs. It can even be seen on lawn furniture and pathways.
Because it’s attracted to the honeydew left behind by sap suckers, sooty mold can affect many tree species.
Sooty mold is primarily a cosmetic problem
By itself, sooty mold won’t hurt your tree as it feeds on honeydew, making it primarily a cosmetic issue. But if it becomes thick enough, it can cause leaf yellowing or stunt the plant’s growth.
Managing sooty mold on trees and plants
The presence of sooty mold on trees and plants indicates that it is, or has been, a sucking insect population. By managing these populations, the problem of sooty mold will eventually go away. Careful pruning by a professional arborist can also remove infected parts if the problem is large enough.
Your arborist may also suggest control methods like dormant oils, and the application of broad spectrum insecticides can prevent aphids build up or control existing populations. Treatments should be prescribed and applied by knowledgeable arborists that are ISA certified and properly licensed. They are trained and certified to use these materials safely.