New Pest Found on Crape Myrtles
Crape myrtles are one of our most commonly planted trees in yards and along streets. They are prized for their beauty and easy care but a new pest has officially arrived in NC. Crape myrtle bark scale has been found in Wake and Iredell counties.
Crape Myrtle Bark Scale was first detected in Texas in 2004 and has spread throughout the south. It is believed to have come from China. Specialist have been watching for its arrival in NC but from the severity of the infestation it looks like it actually arrived many years ago. Crape myrtles are typically almost maintenance free (unless you top them) but now they will require pest management to stay healthy and beautiful.
Crape myrtle bark scale is a felt scale related to azalea bark scale and oak eriococcin scale. They feed on phloem like other “soft scales” causing extensive honeydew deposits. The growth of black sooty mold growing on the honeydew found on the bark is quite noticeable. It is an obvious indicator to alert gardeners to the pest. The presence of the white adult scales on the bark and twigs and the pink blood exuded when crushed are additional distinctive characteristics.
Female scales produce fluffy white filaments that cover their body as they mature. The white threads become felted or matted into thick whitish scale coverings while the adults are attached to the bark. In spring they produce eggs beneath their body before dying. Tiny crawlers hatch from the eggs and move a short distance to settle before producing white filaments. They have at least 2 overlapping generations. At low density, crape myrtle bark scale feed in rough areas around branch collars but as the population increases all the bark may be covered.
If you notice unusually heavy honeydew and sooty mold on crape myrtles, take a closer look at the bark. If crape myrtle bark scale is found, the end result is a crape myrtle that is black in color and produces fewer and smaller flowers. Luckily this pest does not kill trees outright like some other exotic pests.
Crape myrtle bark scale, as with many new nonnative insect pests, has few natural enemies here in the U.S. and can reach very high, damaging populations. There are several species of lady beetles that feed on this pest. Large numbers of lady beetles can usually be found on heavily infested trees, but the population growth tends to lag behind that of the bark scale.
Long-range dispersal occurs through human transport of infested plants. Short-range dispersal can potentially occur by wind or as a result of crawlers being transported on birds or flying insects, as well as by gardeners and landscape maintenance equipment and personnel. Crape myrtle bark scale readily spreads from tree to tree once it becomes established in an area, even when trees are hundreds of feet apart. Consider diversifying the tree planting of your neighborhood to help ensure all the trees are not infested or killed at once by a single pest.
Control programs are still being determined because the pest is so new. Effective treatments may include drench applications of neonicotinoids because they are usually effective against phloem feeders. A complication is that crape myrtles flower continually and attract a large number of pollinators and many labels restrict their use. Another possibility for control is insect growth regulators because they are effective for many other scales.
Research indicates that horticultural oil sprays do not penetrate the felt covering of mature females. Exposed stages including crawlers and nymphs can be reduced with timely sprays. Infested trees can be sprayed with horticultural oil after leaf drop in the fall and again in the spring before bud break. Be sure to follow label directions and do not rely on this dormant oil treatment alone to control the crape myrtle bark scale.
Treatments available do not provide 100 percent control, and must be reapplied each year.