Black Mold on Oak Trees

What we see on oak trees, and other trees, that looks like black mold is actually a fungus called sooty mold.  Maybe that’s bandying semantics, but black mold is what’s found inside homes and buildings, and sooty mold grows on secreted honeydew from insects.

This is a common disease of oaks and several other trees. Various insects, most notably aphid in our area, secrete sticky, sweet honeydew in their infestation of trees. Sooty mold then grows on that honeydew, producing the dark growth we often call “black mold”. 

 The “good news” here is this is largely an aesthetic issue. Since the mold forms on the honeydew, there is little to no damage done to the tree. If a severe mold buildup occurs, it can block sunlight enough to interfere with the tree’s photosynthesis process, which can inhibit good growth.

 The chief key to preventing/controlling sooty mold is reducing the insect/aphid infestations so there’s less secretion of honeydew and consequently less material for the sooty mold to grow upon. Tree injections can be extremely helpful in curtailing these infestations.