Aphids are small, pear-shaped insects that feed on plant sap and excrete sugary honeydew. Honeydew is the waste material excreted by aphids, and this sticky substance can quickly cover a car or landscaping underneath infected trees. Aphids can be green, yellow, black, brown or red and be winged or unwinged. Aphids usually feed in groups and do not move rapidly when disturbed. When a tree is infested with aphids, leaves and the ground under the tree will be covered with honeydew and a black, sooty mold could grow on it. It is best to check susceptible trees often, such as twice a week, to catch aphid infestations early.
Lindens and tulip trees
Spray leaves with water to mechanically remove aphids, or treat the tree with insecticides.