Sooty Mold in Crape Myrtle Trees (S3E8)

Sooty mold can wreak havoc on crape myrtle trees! It is the black, crusty material that covers the leaves during the growing season. Have you ever seen a crape myrtle in the summer with black leaves and even black wood?

What is the cause?

It is caused by tiny little insects, such as aphids and scales, that love crape myrtles. They will suck the leaves for plant juices. As they digest the juices, they excrete a sugary substance that we call honeydew. Your leaves will start out shiny from the honeydew and feel slick, but will start to attract other insects, as well as, sooty mold.

How should I treat sooty mold?

My preferred treatment is to grab something with the active ingredient of acephate. The Acephate 97UP bag shown below is just what we need.

  • Take roughly 4 tablespoons of acephate and mix with 1 tablespoon of water
  • Measure diameter of trunk near the base, just above ground level
  • Double the diameter and paint a band around each truck
  • Treat on May 1 and again on July 1

For example, if you have a trunk that measures 1″ (25mm) in diameter then paint a 2″ (50mm) tall band around the trunk.

Acephate 97UP

Insecticide is systemic meaning that it will move through the tree to the leaves and twigs. When an insect begins to feed on the leaf then it will be killed by the insecticide, and no more sooty mold!

of, relating to, or being a pesticide that as used is harmless to the plant or higher animal but when absorbed into its sap or bloodstream makes the entire organism toxic to pests (such as an insect or fungus)

Definition of ‘systemic’ by Merriam-Webster
Closeup of an aphid. They are small!!

You could also use a granular form of the insecticide that will allow it to be absorbed by the root system, or a trenching method for pouring the solution around the base. This latter method will typically work all season with one treatment.

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