Help! My crape myrtles are turning black

Crape myrtle trees are a beloved staple across Middle Georgia, known for their vibrant blooms that thrive in our hot, humid summers. When properly pruned, they even add a touch of beauty to the winter landscape.

But lately, something’s been off…

Recently the extension office has received several calls from homeowners wondering why their crape myrtle trees are turning black. Many are hoping for a quick, “one-and-done” fix for what looks like a fungal problem.

What they’re seeing is called sooty mold. While it may look alarming, it’s not actually a disease harming the tree. Instead, it’s the result of a relatively recent invasive insect from Asia: the Crape Myrtle Bark Scale.

These tiny pests feed by inserting straw-like mouthparts into the plant and drawing out sugars. Since they consume more than they need, they release the excess as a sticky substance known as honeydew. This coating creates an ideal surface for black sooty mold. The heavier the infestation, the more noticeable the dark coating on the trunk and branches — and sometimes even on mulch or plants below the tree.

While sooty mold is superficial and can be scrubbed away using a soft-bristled brush, water and a small amount of dish soap, this unsightly coating is not the only effect of this pest. Their feeding may also result in delayed leafing in the spring, fewer and smaller flower clusters, and stunted growth. Severe infestations may also cause dieback of tree branches and can even result in total tree loss.

Crape Myrtle Bark Scale appears as small white or gray bumps along branches and twigs, and they tend to congregate around pruning cuts and in the protection of bark crevices and loose bark. The “bumps” are older nymphs and adults. They tend to favor susceptible trees growing in shady locations and those weakened by over-pruning, though any crape myrtle variety can be vulnerable. Currently, no crape myrtle variety is known to be resistant to this scale.

This insect has three stages: eggs, nymphs and adults. Each female can lay as many as 300 eggs in a sac. Eggs hatch in the spring, and in our area, a second-generation hatches in late summer. The tiny “crawlers” are the only mobile stage; after their first molt, they lose their legs and remain in place.

If you have one or more crape myrtle trees in your landscape, you will want to monitor them for Crape Myrtle Bark Scale. Small problems are much easier to control than big ones!

Lady beetles do help by feeding on these pests, but unfortunately, scale populations can grow faster than their natural predators can keep up.

For long-term control, insecticides are necessary. Because most life stages are protected by a waxy coating, sprays are usually ineffective except against the crawler stage. The most effective approach is applying a systemic soil drench between late March and May. Look for active ingredients such as imidacloprid, dinotefuran or clothianidin.

However, since these insecticides, especially imidacloprid — can be harmful to foraging pollinators, it is imperative to heed the warnings on the package label and carefully follow dosing recommendations. Other insecticide options are available by contacting a licensed commercial pesticide applicator, especially when treating larger trees.

Because this pest spreads easily, it’s wise to treat nearby crape myrtles if one tree is infested, even if they appear to be free from attack. Plant entomologists recommend carefully monitoring infested trees and treating to control this insect for at least one additional season. 

For more information about this serious insect pest, see this University of Georgia resource. 

Kathy Hensley works for the University of Georgia Cooperative Extension Service in Bibb County. The county office provides resources for gardeners as well as educational services and community support. Visit their office at 715 Oglethorpe Street, call them at 748-310-5350or email their staff at bibb.extension@uga.edu.