Maria is a master gardener and master of public health. She & her husband, known online as The Gardener & The Cook, live in coastal Alabama.
There is a relatively new pest among Crepe Myrtles. I say “relatively” because it has recently reached my home state of Alabama only within the last couple of years. It reached my garden early this year (2022). It is called Crepe Myrtle Bark Scale, or CMBS, Acanthococcos (Eriococcus) lagerstroemiae Kuwana (Hemiptera: Sternorrhyncha: Eriococcidae).
The scales are brown and more difficult to see, but the eggs are a bright white. I first learned of it when it was mentioned in a lecture I attended in March of this year. At the time, we were told not much was known about it. I did know, however, that it was on some of my crepe myrtles.
After getting photos and a question from a reader asking, “What’s wrong with my crepe myrtles?” I began researching CMBS myself. Most importantly, I learned it will not kill these trees, but will reduce the amount and size of their flowers. I learned it was first discovered in Texas in 2004. By 2015, it had crossed through Louisiana, and reached Mississippi. It is now in fourteen states, and Washington, D.C.
Was a Newly Purchased Myrtle Already Affected?
I first saw it on a young Natchez Crepe Myrtle tree we purchased last summer, and planted in our front yard. The disease/pest didn’t appear until a few months later, then spread to another two in our front yard. The much older ones in the side and back yards are unaffected, so far, but I have found it on some very young myrtles that came up from seed. This leads me to suspect the new one may have been sub-clinically diseased when we bought it, but we’ll never know for sure.
Sooty Mold Is Always a Symptom to Watch For
The black sooty mold on the trunks and branches are characteristic of infestations by several pests, including scale, mealy bugs, and aphids. The mold occurs on the poop of insects. Because the poop is sweet it is called honeydew. Also because it is sweet, ants eat it, but they can’t eat it fast enough. So it molds and turns dark black.
If there is a plus-side to the black mold, it is that the white scales are easy to see on the dark background. So, what to do?
Two Steps To Getting Rid of These Critters
- First, get a pan or bucket of warm soapy water. Soap. Not detergent. Wearing gloves and using a soft cloth, gently rub the mold off the limbs. It may be necessary to do this more than once.
- Next, treat the scale. There are several products that can be used to kill the scale. In late March through early May, the trees should be treated with any one of these systemic products.
- Imidacloprid (sold under the trade names of Merit, and Bayer Advanced Tree & Shrub Insect Control).
- Thiomethoxam (sold under the trade name of Meridian).
- Dinotefuran (sold under the trade name Greenlight Tree & Shrub Insect Control with Safari).
I have not listed the products in any particular order. As far as I know, any one is as good as the others. The directions for these products will probably vary, but each should tell you to mix a certain amount with water, and use a gallon (or gallons) based on the circumference of the tree trunks.
Be aware, some of these methods of control can be harmful to bees, so read the labels carefully.
Finding the Liquid Form May Be Difficult
I shopped for these in liquid form, but could find them only at wholesale stores in huge amounts for around $200. I finally found a product containing imidacloprid at a big box store in granular form. It was the Bayer Advanced Tree & Shrub Insect Control mentioned above.
We all know granular products are slow-release. I wanted quick action, so I dissolved the prescribed amount in a gallon of water, then poured it around the affected trees. It will probably require more than one treatment — I’m waiting to see about that.
How Systemic Products Work
Systemic products of this type, whether liquid or granular, are poured on the ground around the plant, and taken up through the circulatory system, just as nutrients and water are. When using these and other pesticides and herbicides, be sure to wear rubber gloves, protective clothing, and eye protection.
Research on horticultural pests are ongoing at land grant universities and at companies producing these products. There are agricultural grad-students involved in this research all over our country, and more is being learned about this and other gardening problems every day. Here’s hoping they learn more about this problem soon before we start seeing crepe myrtles compromised everywhere.
Overplanting Causes Problems
One reason trees and shrubs are compromised is when they are over planted. That happened many years ago with Red Tips (Photinia × fraseri). More recently it has happened with Bradford pears (Pyrus calleryana) and Indian Hawthorn (Rhaphiolepis indica). Crepe Myrtles (Lagerstroemia indica) have also been over planted because we love them. Let’s hope we don’t love them to death.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2022 MariaMontgomery