Often we have no idea what is happening up in the canopy of our trees. Insects are born, live and die with us being none the wiser. However, one group of insects often give themselves away in a rather annoying way – by defecating, a lot. Aphids and their plant feeding relatives are so well known for their excrement that we have even come up with a more pleasant term for it – honeydew. Honeydew is produced by aphids and soft scales and is basically the plant sugars that end up passing through the digestive system of sap feeding insects.
Right now maples and oaks have aphid populations high enough to produce noticeable amounts of honeydew. The aphids are small and green and would remain unnoticed except for the sticky film they leave. Aphids do not harm a healthy tree and no management is necessary. A fungus called black sooty mold is commonly associated with aphid honeydew and is often more damaging to the plants than the aphids. The sooty mold coats the leaves with the honeydew and prevents sunlight from reaching the leaves. Usually this becomes more of a problem when we go a long period without rain to wash off the honeydew.
Aphid honeydew can become bothersome if it is coating decks, furniture or vehicles. It is generally not feasible to try to control aphids in a large tree. Aphids are difficult to control and specialized equipment is needed to reach up into the canopy. There is some satisfaction from just blasting the tree with water in order to dislodge aphids and can reduce populations temporarily.
If aphid honeydew has been accumulating on your car you may know how difficult it is to remove that sticky film. This website from the University Of Minnesota gives some useful tips on methods to remove honeydew.