How to Control Sooty Mold on Crape Myrtles

What Causes the Sooty Mold to Develop?

The sooty mold on your crape myrtles is caused by a sap-feeding insect, known as Crape Myrtle Bark Scale (CMBS). The insect’s excrement, known as honeydew, is sugary. Eventually, the sugary honeydew becomes moldy, turning the beautiful limbs of a crape myrtle dark and sticky.

Crapemyrtle with Black Scale
Sooty Mold on a Crape Myrtle in North Texas.

Like any mold, it can be cleaned up with mild dish soap and water. However, a little cleaning will not eliminate or control the problem: a CMBS infestation.

How to Control CMBS Infestation

CMBS can be controlled by systemic insecticides or by the help of lady beetles. While Lady beetles are a fine organic, natural solution, lady beetles do not multiple as quickly as CMBS. They are not as effective as systemic insecticide treatments, especially if the CMBS numbers are high.

There are several commercial CMBS treatments available. However, we recommend that you consult with an ISA certified arborist experienced in treating CMBS infestation. A follow-up treatment one year after the initial treatment is recommended. Occasionally, the best solution is to have the tree or trees destroyed.

Treatment Basics

  • Treatments should be done during the active growing season: March to May
  • Treat nearby apparently non-infested crape myrtles
  • Expect the treatment to take several weeks to have an effect
  • Sooty mold must be washed off, as well as the dead CMBS
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Krista White

Krista is a member of the marketing and education team at Tree Shepherds. A lifelong learner, she loves writing about anything from Hemingway to Quercus macrocarpa.