Preventing and Controlling Sooty Mold Tree Disease

Sooty mold appropriately and exactly describes the disease, as it looks just like chimney soot.  Ascomycete  fungi, which includes many genera, commonly  Cladosporium  and  Alternaria are usually the offending fungal organisms.  Although unsightly, it seldom damages the tree but it can look nasty in the landscape. The pathogens are dark fungi growing either on the honeydew excreted by sucking insects  or on exuded sap  material coming from leaves of certain trees. These sucking insects can include aphids and scale insects and sooty mold may occur on any tree but is most commonly seen on boxelder, elm, linden, and especially  maple trees. More on Honeydew Honeydew is a sugary,  sticky liquid secreted  by sucking, piercing  insects as they feed on plant sap. The insect feeds itself by using a special mouthpart that penetrates  the soft tissues of plant foliage, soft stems and most particularly for aphids, the tender underside of leaves. These soft-bodied insects produce the honeydew as a liquid waste product via the gut but will not harm your tree. Its a real problem on  everything beneath and around the tree that is exposed to the syrup and then colonized by sooty mold. Prevention of Sooty Mold Sooty molds are associated with high temperatures and increased stress brought on by limited moisture. During drought, aphid populations and their honeydew production typically increase on foliage undergoing moisture stress. One prevention method for the mold is keeping plants and trees well-watered and controlling the soft-bodied insect population is very important. Control of Sooty Mold Sooty molds can be indirectly controlled by reducing populations of sucking insects that excrete honeydew. Use the appropriate recommended chemicals that control aphids and other sucking insects. The appropriate chemicals  your trees need for these sucking insects might be applying horticultural oil  during the dormant season  followed by an insect growth regulator in the mid-summer. Also, a good washing of infested trees foliage (if possible) can dilute the honeydew and wash off the mold. This alone may be all that is needed.