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 tree. 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 impact.
As with any new non-native insect, CMBS has few natural enemies here in the U.S. and this is why they are able to reach such high damaging populations in a very short period of time. It is not unusual for tender new growth and small branches to be completely encrusted with scale. The CMBS produce large quantities of a substance called honeydew and this result in heavy accumulation of sooty mold on the leaves, branches, and trunks of infested plants. We have also seen this black mold on underlying plants and mulch where the honeydew has dripped out of infected trees. The end result is a Crape Myrtle that has turned black and ugly, due to heavy sooty mold accumulation, and doesn’t produce normal amounts of foliage and blooms. Sooty mold is not a definite indication of CMBS, but if you find white, felt covered scales that bleed pink when punctured, you can be sure you’ve found Crape Myrtle Bark Scale. There are several species of lady beetles, including several non-native species that feed on CMBS in the larva stage. Although these lady beetles can help reduce the number of CMBS, their numbers are not great enough to completely eliminate CMBS from the landscape.
Crape Myrtle Bark Scale belongs to a special group of scale insects 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 from 3 to 4 generations per year, which leads to an almost explosive growth pattern in a very short period of time. Eggs hatch quickly into tiny pink crawlers, and the older nymphs turning a darker gray or brown color. Adult males, which are rarely seen, are winged and mobile. Short range dispersal can potentially occur by wind, as a result of crawlers transported by other insects or birds, or by landscape maintenance equipment and personnel. CMBS rapidly spreads from tree to tree once it becomes established in an area, even when trees are hundreds of feet apart.
In order to treat for CMBS, we have to look to areas that have had to deal with this infestation longer than we have. The trial and error of different insecticides and various application methods have already been done. The proven method of treatment for all 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 to be unsuccessful. A spray will only kill crawlers and nymphs and can not penetrate the felt covering on the female. The level of effectiveness of spray over drench will leave much to be desired. Although the cost of drench initially may be a little more than the cost of a spray, you will only have to drench one time a year, which will dramatically reduce the amount of money and effort needed to fight this infestation.
To receive optimal results from Systemic Drench insecticides:
- Treat anytime during the growing season. Best if applied 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 will equal the total number of ounces you will need to treat your tree.
- Measure your trees prior to purchasing product. Estimating the size of your tree could lead to under treatment and will not give you optimal results.
- 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 gaining a foothold in your landscape again.
Application rates of systemic insect control products will vary greatly depending on the size of your trees. Rates for shrub type Crape Myrtles will vary from that 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 you will need. We at Dan West recommend Ferti-Lome brand Tree and Shrub Drench. This product has a proven track record for helping homeowners to eliminate CMBS from their landscape. The application process is very simple; you will need access to water and an old 5 gal. paint bucket will be helpful.
Although dormant horticultural oil sprays have not been fully tested against CMBS, and it’s difficult for the 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 and/or again in the spring before bud formation. Such treatments are most useful on trees that were 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.
Once control is obtained, many homeowners desire to remove as much sooty mold as possible to improve aesthetics. 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 treated is the most effective way to keep the trunks and surrounding landscape free from the unsightly mold.