Crape Myrtle Bark Scale Scouting and Control Recommendations

Blake Layton, Extension Entomology Specialist

Crape myrtle bark scale is now present in Mississippi. Our own Dr. Gary Bachman recently discovered a well-established infestation in Ocean Springs (March, 2015). This non-native scale is a serious threat to southern crape myrtles; it threatens to turn what has historically been a beautiful, low-maintenance landscape tree into an unsightly, high maintenance landscape tree! Because of this threat, we need to continue to be alert for crape myrtle bark scale in other areas of the state and control it aggressively if detected.

Crape myrtle bark scale, Eriococcuslagerstroemiae, first appeared in Texas in 2004 and has since moved into Oklahoma, Louisiana, Arkansas, Tennessee (Memphis area), Alabama, and Georgia. Mississippi is now added to the list of infested states, and we are asking for your help in continuing to look for this pest in other counties.

One of the best ways to determine if/when crape myrtle bark scale is present in your county is to:

1} learn to recognize this pest yourself and be alert for infested plants

2} enlist the aid of Master Gardeners in your county, ask them to notice problems on crape myrtles and report any detection of crape myrtle bark scale.

3} enlist the aid of local nurseries as well as other “plant people” and naturalists

Crape myrtle bark scale is pretty easy to spot and identify. Here’s what to look for:

1} Crape myrtles with heavy accumulations of black sooty mold on the trunk

2} Crape myrtles with patches of white felt like material on the twigs and trunk, especially around cracks and crevices in bark and around pruning scars.

3} Adult female scales are covered with a soft, off-white felt-like material and are about 1/10 inch long.

4} Use a toothpick, knife point,or small twig to break the felt-like covering and the insects will bleed red or pink, or you may actually see the pinkish eggs or crawlers underneath.

Note: crape myrtles that have or had heavy infestations of aphids will also have heavy accumulations of sooty mold on the trunks, but they will not have the other symptoms.

Please let us know if you find this insect in your county, take a few pictures, collect a sample of the adult scale, preserve in alcohol, and mail it in. Also phone the Bureau of Plant Industry at 662-325-3390 and report possible detections. Please include information on where and when the sample was collected.

Biology: Crape myrtle is the only known host of this insect. Based on information from similar plant growth zones in China and observations reported from other infested states here in the US, it appears that CMBS will complete two to four generations per year in the Southeast. Eggs and mature females are the most common stage for overwintering, but overwintering can occur in all life stages. This insect does not spread by flying as only male CMBS have wings. 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 the feet of birds or flying insects.

Control: Crape myrtle bark scale is going to be a difficult pest to control. Initially, homeowners and landscape managers will likely want to be very aggressive in trying to control isolated infestations, with the goal of eliminating the infestation before it can spread to other crape myrtles in the landscape. When possible, destroying infested plants, in a manner that will prevent spread of scale to nearby crape myrtles, may well be the best response. This is most practical for small, recently-installed plants.

This pest is so new that control programs are still being developed, but the following are some of the most useful treatments being used in other states. Note that some of these treatments are commercial products, and homeowners are encouraged to seek assistance from licensed commercial applicators to control CMBS, especially for treating larger trees. “Aggressive control” of CMBS involves using a combination of the following treatment methods, especially including an application of soil-applied systemic insecticide and a series of treatments with acephate and/or the growth regulator products. To assure complete control, infested trees should be carefully monitored and treated for at least two seasons following initial treatment. Even if treated trees appear to be free of CMBS after the first season of treatment, they should at least be treated with one of the soil-applied systemic insecticides in the second year and monitored closely for recurrence of CMBS.

Crape myrtles that appear to be uninfested, but are located near infested trees (within 30 feet or so) should be treated as if they are infested because new or low-level infestations are difficult to detect. Also, consider treating all crape myrtles in a landscape where a CMBS infestation has been found with a preventive treatment of one of the soil-applied systemic insecticides.

Treatment Program Options for Crape Myrtle Bark Scale:

-- Use a soft bristle brush, water, and a bit of dish washing liquid to scrub heavy accumulations of scale and sooty mold from trunks of heavily infested trees. Although CMBS also occurs higher in the tree on twigs and limbs that can’t practically be washed, this trunk washing will improve appearance of the tree and make it easier to monitor the long-term effectiveness of the treatment program (Do mature female scales reappear on the trunk or does more sooty mold build up on the trunk?).

-- Treat infested trees with a soil-applied systemic insecticide containing imidacloprid (Merit, and Bayer Tree and Shrub Insect Control are examples) or dinotefuran (Safari and Greenlight Tree and Shrub Insect Control are examples). This treatment should be applied in late spring before trees begin to bloom (late April-May). Be sure to observe pollinator protection precautions specified on the label. These soil-applied systemics are the most effective and easiest to apply treatments available for CMBS, but these treatments may only be applied one time per season and are not likely to give 100% control when used alone. Be sure to retreat with a soil-applied systemic the following year, even if there are no signs of continued infestation because low level infestations are difficult to detect.

-- Apply foliar sprays of acephate (Orthene Turf Tree and Ornamental 97 Spray and Bonide Systemic Insect Control are examples) to control crawlers and newly settled nymphs. Although acephate sprays will also eliminate beneficial insects such as lady beetles, they are useful for supplementing control provided by soil applied systemics, especially when applied as a series of repeated sprays (label allows application at 14 day intervals). The label for Orthene TTO also allows application as a “paint on slurry” to a band of bark around the lower portion of the trunk(s) (see label for details). Acephate is systemic and can be absorbed through the bark and translocated to the upper portions of the tree. This may be a useful method for treating treeswhere foliar sprays are not appropriate due to drift concerns. Be sure to observe pollinator protection precautions when using acephate; do not treat when plants are blooming.

-- Apply foliar sprays of insect growth regulators containing pyriproxyfen (Distance) or buprofezin (Talus) when crawlers are active. Although not yet fully tested against CMBS, these growth regulators are effective against crawlers of many other scale species and are less disruptive of biological control than acephate. Note that each of these products is limited to only two applications per year, but it is permissible to use two applications of Distance and two applications of Talus.

-- Spray infested trees with horticultural oil after leaf drop in the fall and/or again in the spring before bud break, being sure to observe label directions regarding temperature and application rates. Although dormant oil sprays have not been fully tested against CMBS, and it is difficult for the oil to penetrate the felt covering of mature females, dormant oil treatments should help control the more exposed stages, such as crawlers and young nymphs.

Thanks for your help!