Crape Myrtle Bark Scale (CMBS) is a serious threat to our favorite Mid-South tree, the Crape Myrtle. It threatens to turn what has historically been a beautiful, low-maintenance tree into an unsightly, high-maintenance one. This non-native scale was first reported in the U.S. in 2004 in Texas, was first found in Shelby County in 2013, and will likely continue to spread. All members of the gardening community need to know how to identify and control CMBS to help slow the spread and reduce its impact.
What Is Crape Myrtle Bark Scale?
As with any new non-native insect, CMBS has few natural enemies here in the U.S., which is why populations can reach damaging levels in a very short period of time. It is not unusual for tender new growth and small branches to be completely encrusted with scale.
CMBS produces large quantities of a substance called honeydew, which results in heavy accumulation of sooty mold on the leaves, branches, and trunks of infested plants. This black mold can also appear on underlying plants and mulch where the honeydew has dripped from infected trees. The end result is a Crape Myrtle that has turned black and ugly due to heavy sooty mold accumulation, and that does not produce normal amounts of foliage and blooms.
Sooty mold is not a definitive indication of CMBS, but if you find white, felt-covered scales that bleed pink when punctured, you can be sure you have found Crape Myrtle Bark Scale. Several species of lady beetles feed on CMBS in the larval stage, but their numbers are not great enough to completely eliminate CMBS from the landscape.
How CMBS Spreads
Crape Myrtle Bark Scale belongs to a special group known as felt scales. Adult females produce a white felt-like sac around their bodies and lay approximately 100 to 300 pink eggs inside this sac. Based on information from other infested states with similar growing conditions, CMBS will complete 3 to 4 generations per year, leading to an almost explosive growth pattern in a very short period of time. Eggs hatch quickly into tiny pink crawlers, with older nymphs turning a darker gray or brown color. Adult males, which are rarely seen, are winged and mobile.
Short-range dispersal can occur by wind, by crawlers transported by other insects or birds, or by landscape maintenance equipment and personnel. CMBS spreads rapidly from tree to tree once established in an area, even when trees are hundreds of feet apart.
How to Treat CMBS
The proven method of treatment for CMBS is the use of a root drench systemic insecticide. This type of insecticide is poured on the soil, picked up by the roots, and distributed through the vascular system of the tree. As the CMBS feed on the tree, they ingest the insecticide and are killed off. Only those insects that attach and feed will be eliminated using this method.
Attempting to use a spray to eliminate CMBS has proven largely unsuccessful. A spray will only kill crawlers and nymphs and cannot penetrate the felt covering on the female. Although the initial cost of a drench may be a little more than a spray, you will only need to drench once a year, which dramatically reduces the amount of money and effort needed to fight the infestation.
Treatment Instructions
Treat anytime during the growing season. The best time to apply is late February or early March.
- Treat nearby uninfected trees within the landscape.
- Measure trunk circumference at approximately eye level.
- If multiple trunks are present, measure all at eye level.
- The total number of combined inches of circumference equals the total number of ounces of product you will need.
- Measure your trees before purchasing product. Estimating the size could lead to under-treatment.
- Expect it to take several weeks before control is obtained.
- Do not expect sooty mold to disappear overnight.
- Treat again yearly to keep CMBS from regaining a foothold in your landscape.
Application rates will vary greatly depending on the size of your trees. Rates for shrub-type Crape Myrtles will vary from those of tree-form types. Once you have measured your trees, bring those measurements to Dan West Garden Center and we will assist you in determining the correct amount of product. We recommend Ferti-Lome Tree and Shrub Drench, which has a proven track record for helping homeowners eliminate CMBS from their landscape. The application process is very simple: you will need access to water and an old 5-gallon paint bucket is helpful.
Dormant Oil Sprays
Although dormant horticultural oil sprays have not been fully tested against CMBS, and it is difficult for oil to penetrate the felt covering of mature females, oil treatments have been shown effective in controlling crawlers and nymphs. Spray infested trees after leaf drop in the fall or again in the spring before bud formation. Such treatments are most useful on trees found to be infested too late in the year to use soil-applied systemic treatments. Do not rely on oil-based sprays alone to control CMBS.
Removing Sooty Mold
Once control is obtained, many homeowners want to remove as much sooty mold as possible to improve the appearance of their trees. A soft-bristled brush with a mixture of mild dishwashing soap and water will help remove some of the dark mold. However, keeping your trees consistently treated is the most effective way to keep trunks and the surrounding landscape free from the unsightly mold.