Tuesday, March 4, 2014

A New Pest on the Loose: Crape Myrtle Bark Scale

There's a new garden pest on the loose. It's an insect called Crape myrtle bark scale (CMBS), and it's spreading very quickly across the southeastern U.S. Crape myrtle bark scale was first observed near Dallas, TX in 2004, and it's spreading eastward.

CMBS appears as white or grayish felt-like encrustations on the wood. At first they may be found in branch crotches or near pruning wounds, but heavy infestations are capable of covering the tree.

Since most gardeners don't spend much time inspecting crape myrtle crotches, the adult insects are usually missed until black sooty mold is discovered. Sooty mold is a black, powdery fungus that is usually associated with aphid infestations, so the real culprit may not be identified correctly.

Crape myrtle bark scale probably won't destroy our crape myrtles, but a heavy infestation and all that sooty mold sure will make them look ugly. It also stands to reason that a ton of insects sucking on the trees and sooty mildew coating the leaves can weaken them.

There are a few things you can do to combat CMBS:
  • Be aware that CMBS may target hybrid crape myrtles first. If you have hybrids, check them closely every now and then.
  • Look for black sooty mold on the bark, remembering that sooty mold may result from aphids and CMBS.
  • Washing the trunk and limbs as high as you can reach, working with a soft brush and dishwashing soap. This will help to remove female scales, eggs and the black sooty mold.
  • Though horticultural oil spray hasn't been shown to be effective, it sure can't hurt. Horticultural oil works by covering the scales and suffocating them. Spray with enough force to get the oil under loose bark and into tight crevices. Spray thoroughly.
  • Winter is a very good time to wash your trees and spray with horticultural oil because the leaves are off and it's easier to see what you're doing, and higher application rates can be used without hurting the plant.
  • Systemic insecticides applied as a soil drench are known to be effective. Be sure to read and follow all label instructions. It's best to spray during May or June. Don't expect instant results because it will take a few weeks for the chemical to spread throughout the plant.
  • If you prefer to avoid systemic insecticides, let lady beetles do the work. Lady beetles love to eat aphids and baby scales.

For more information, check out the following links:

• Texas A&M: http://bit.ly/MBlyAJ
• The Crape Myrtle Trails of McKinney (otherwise known as the “crape myrtle city”): http://bit.ly/1bmJW4f
• LSU Ag Center: http://bit.ly/1fAdLtT

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