Crape Myrtle Bark Scale By Mario Villarino

This week, several reports of crape myrtle bark scale has been reported by concerned citizens of our county. According to Dr. Mike Merchant, Crape myrtle  bark scale is a a relatively new insect pest is troubling crape myrtle in north Texas cities and backyards.  Although an official name has yet to be given, this insect is thought to be an exotic pest that has somehow found its way to north Texas. In the genus Eriococcus, the scale is a type of felt or bark scale.  It’s closest cousin is the Azalea bark scale, but that species has never been associated with crape myrtle before.  Current evidence suggests that the scale may be a migrant from Asia, Eriococcus lagerostroemia, which is common on the timber tree Lagerostroemia indica in Japan and China.One of the first signs of a bark scale infestation is a black (sooty mold) coating that appears on the bark of the trunk and on the branches of crape myrtles (see picture). Leaves and limbs may feel sticky from byproducts of the insect’s feeding. The insects appear as white, waxy encrustations likely to occur anywhere on the plant, but often near pruning wounds or in branch crotches. Up close, the azalea bark scale-insect is white to gray in color. Larger female scales “bleed” a pink liquid when crushed. Careful examination may reveal dozens of pink eggs under some of the larger white scale covers.

Control recommendations for azalea bark scale are still being developed; however, our current best suggestions for control of this insect include:

  • For heavily infested plants wash the trunk and reachable limbs with a soft brush and mild solution of dishwashing soap. This will remove many of the female scales and egg masses and make insecticide control more effective. Also, washing will remove much of the black mold that builds up on the bark on infested trees.
  • Horticultural oil has not yet been shown to be effective against this insect, however a winter application of dormant oil to the bark and crotches of the plants where scales shelter may be beneficial. Winter is an especially good time to treat for scales because a higher (winter) application rate can be used without damaging the plant. Thorough coverage of the tree is especially important when treating with oil.
  • Application of systemic insecticides as a drench applied to the root zone of plants to be protected has shown the most promise in tests to date. Imidacloprid (Merit® or Bayer Advanced™ Garden Tree and Shrub Insect Control) and dinotefuran (Greenlight Tree and Shrub Insect Control with Safari) has shown best control when applied between May and July. When drenching the soil with a systemic insecticide, allow several weeks for control as the products needs time to spread throughout the plant.

As the crape myrtle bark scale spreads throughout Texas, one of the first questions we hear is “will the scale kill my tree?” The answer appears to be “no”, at least not often.  To date we’ve not been able to show any crape myrtle tree death as a result of a bark scale infestation.  But like many sap-feeding scale insects, these little scales can stress and reduce the appearance of the trees, while producing a prodigious amount of sticky “honeydew” that can coat the leaves and anything under the tree (including freshly washed cars). Thanks to Drs. John Hopkins and Jim Robbins of the University of Arkansas Cooperative Extension Service, we can now show you what we believe is likely to be another impact of these scales on trees–namely, smaller flower clusters and reduced blooming.   The other question we are getting is: “If I treat my crape myrtles with a neonicotinoid insecticide, is it likely to affect the honey bees around my home?”  While there is growing concern about the impact of soil-applied neonicotinoid insecticides on honey bee and pollinator health, crape myrtles do not appear to be highly attractive to bees (entomophilic).  Currently we don’t believe that a properly applied soil insecticide (following label directions) will have any significant impacts on foraging bees.  But if anything changes in that formula, we’ll be sure to let you know.  We are also continuing to look for less susceptible varieties of crape myrtle and safer, less expensive treatments for this scale. For more information on this or any other agricultural topic please contact the Hopkins County Extension Office at 903-885-3443 or email me at [email protected].

Upcoming events :

  • Cattlemen Classic and Ribeye Cook-off. October 6, 2017, downtown Sulphur Springs. A great opportunity to learn and enjoy the beef industry in Hopkins County. We will host a producer trade show with companies and support industry (starting at 2:00 PM) at the downtown area (free), a feature keynote speaker Trent Loos at the Courthouse (free) as part of the 2017 NETBIO producer meeting. The celebration continues with the cook-off competition, dinner (tickets available for $25 at Texas Heritage Bank and Brookshire’s in Sulphur Springs) and a free concert featuring Stoney Larue starting at8:00 PM.
  • Red Alliance Red Angus Production Sale.  Registered Bulls, Females, and Commercial Red Angus.  Oct 2, 2017 in the Hopkins County Civic Center. Sale starts 10 am / 150 head can be previewed on Sunday afternoon.  Call John Macek @903-348-2138 for a catalog or www.redalliance.biz
  • Private Applicators CEU and Hamburger Cook-Off. November 1, 2017. Join us to learn new techniques in weed management in pastures (1hr)  hay production (1 hr), pond weed management (1 hr), Laws and Regulations related to use of restricted pesticides (1 hr), and protection of pollinators in agriculture (1 hr. IPM). Regional Civic Center. Call The Hopkins County Extension office at 903-885-3443 to register. Cost $30 lunch included.

 

For more information on these or any other agricultural topic please contact the Hopkins County Extension Office at 903-885-3443 or email me at [email protected].

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Mario Villarino DVM, Ph.D.
Hopkins County Extension Agent for Ag and NR
1200B Houston Street
Sulphur Springs, Texas 75482
903-885-3443

Author: Savannah Owens

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