Crape Myrtle Bark Scale: Information and Treatment Suggestions
Does the trunk of your crape myrtle look something like the picture shown? Is the bark covered in a black film? If so, your crape myrtle may be infested by crape myrtle bark scale (CMBS).
First off, there is no need to remove your trees if you see this. The scale will NOT kill your trees and the black sooty mold is harmless. However, this pest can reduce the amount and size of the blooms and the sooty mold can make your tree less attractive.
It is expected that CMBS is here to stay, but by being proactive you can lower the number of scale insects on your trees through responsible and targeting management.
The black sooty mold CMBS leaves behind is harmless, but many people don’t like the way it looks. If desired, you can remove sooty mold with a dish soap solution and soft-bristle scrub brush. To treat, at anytime of year, mix dishwashing soap with water and scrub the branches with a brush. Although this step isn’t completely necessary, it can reduce female scale insects and egg masses and make chemical controls more effective.
Dawn dish soap, water, and a soft-bristle scrub brush can rid the bark of the sooty mold and honey dew temporarily. A 2% solution (about 2.5 tablespoons soap per gallon of water) is ideal. Stronger solutions could burn foliage if they come into contact with it.
Winter/Early Spring (February - April)
Apply dormant Horticultural Oil to kill CMBS eggs. Crape Myrtle Bark Scale eggs overwinter in tiny waxy egg sacs. The best thing you can do this time of year for CMBS is dormant oil application. You can do this type of application yourself or hire a tree care company to do it for you. Read and follow your dormant oil label closely, since formulations can vary.
With good coverage, dormant oil will coat and kill most CMBS eggs. If any adult and juvenile pests are still present, dormant oils will smother them and decrease their ability to feed. The excess oil evaporates and dissipates quickly, so there is no toxic residue. Horticultural oil is considered safe to use around humans and pets.
Horticultural oils need to be sprayed directly on the pests or eggs to be effective. Since CMBS populations tend to be greater around branch crotches, make sure to get good coverage in these areas.
Spring and Summer
Chemical control may be desired if the infestation is great on your tree. It is highly recommended that you hire a professional to use systemic insecticides and insect growth regulators targeting specific stages of the CMBS life cycle. Remember, chemicals can harm pollinators and bees. Timing chemical treatments is difficult due to complex scale life cycles and a long summer bloom period for crape myrtles - companies with NC Licensed Pesticide Applicators and ISA Certified Arborists on staff are your best bet.
As a DIY job, you can apply a Systemic Insect Drench which can be found at Lowes or online (like Ferti-lome). Mix with water as directed, and apply in a band along the drip line of the tree.
An alternative to chemicals, and a possible DIY summer project, is to apply “summer” horticultural oil to your crape myrtles. Spray it on the bark only to suffocate the tiny insects (if you spray the leaves, they can burn with the heat and sun of summer). Unfortunately, your tree won't look any different after you spray the oil (see below on how to get rid of the black sooty mold), but it'll slow or stop the infestation for now.
For other resources, visit https://thegoodearthgarden.com/control-crapemyrtle-bark-scale/