QUESTION: We have a question regarding one of our large hackberry trees. It’s covered with little white flying bugs and the leaves have a sticky residue. What causes this and is there something that we can do about it?
The bugs you are seeing are called Asian wooly hackberry aphids, and they seem to make an appearance about this time every year. They feed exclusively on hackberry trees, and like all aphids, they feed by piercing the leaves and extracting the juice. The sticky residue is what they excrete after feeding on the leaves, a substance called honeydew. Another byproduct you may notice is a black mold that grows on the honeydew, which is called sooty mold.The aphids apparently do not do enough damage to harm the tree, they are just a nuisance, mostly in late summer and early fall when their population grows due to the many generations that have been produced. If it’s a nuisance you can’t tolerate for some reason, there is a systemic insecticide product that is said to be effective in controlling aphids, but it would not do anything to solve this year’s population. There are several brands available, but the main ingredient is a chemical called imidacloprid, and it should be applied to the ground around the tree in early spring, where it will be taken up via the tree’s vascular system into the leaves.
Not much, then, can be done about this year’s population of hackberry aphids. Hose off the cars, the deck, the lawn furniture and anything under the trees that are sticky from the honeydew, and take comfort in the knowledge that they are a temporary annoyance, and will be gone in a few weeks.