The major insect pest of crape myrtles in Gainesville Florida landscapes are crape myrtle aphids. Crape myrtle aphids secrete sticky honeydew from mid-summer on through winter, which sooty mold grows in the honeydew.
Crapemyrtle Aphids are Gainesville Lawn Pests that have a narrow host range and is the only aphid species that feed on crape myrtles. Crape myrtle aphids are found from May through September, with peak populations during July and early August. Crape myrtle aphid adults and nymphs are pale yellow-green with black spots on their abdomens. They range from 1/16- to 1/8-inch in length. These aphids generally feed on the undersides of crape myrtle leaves. They feed by inserting their needle-like mouthparts into the soft tissues and extracting plant sap. As aphids feed, they inject saliva into the leaf tissues, which, in turn, causes yellow leaf spots to develop. Heavy infestations can deform leaves and stunt new growth. Buds, branch tips and flowers can also be damaged by the feeding injury.
In addition to direct damage, aphids can damage plants indirectly by secreting honeydew, a sugary bi-product of their feeding. Honeydew is a perfect substrate for the growth of sooty mold fungi and a source of food for other insects such as ladybugs, ants, wasps, and flies. Although unsightly, sooty mold itself does not directly harm the crape myrtle. Instead, it shades the leaves and interferes with photosynthesis. Under heavy infestations, sooty-mold-covered leaves may drop many weeks prematurely. Even the twigs and stems of the plants may be coated in the black sooty mold. That becomes more evident as the plants defoliate.