Friday, April 4, 2014

New pest on crape myrtle

Texans (and many other southerners) love their crape myrtles! And why not? Crape myrtle (Lagerstroemia species) is one of the few trees that bear colorful flower displays through much of the summer, come in a variety of stunning colors, is easy to grow, and until now has been relatively pest free. Unfortunately, the pest-free reputation is changing with the advent of a new exotic scale pest.

Crape myrtle trees infested with CMBS in Richardson, TX.  Black sooty mold
 deposits on the branches and trunks of infested trees are often the first
sign of an infestation.  Note the white, scale encrusted upper branches. 
In 2004 I received a call from a local lawn maintenance company that was having a difficult time controlling an unusual scale on crape myrtle at a commercial property in Richardson, TX. After examining it I thought this scale might be something new, and sent samples of the insect off to experts for identification. Under the microscope it appeared to be a Eriococcid scale called azalea bark scale, Eriococcus azaleae.  Azalea bark scale is a common pest of azaleas in the eastern U.S.,  but had never been recorded as occurring on crape mrytle before. A suggestion by a retired USDA scale specialist led us to change our minds and believe that the scale might actually be a closely related scale known as Eriococcus lagerstroemia. This scale is an important pest of crape myrtles in China, Japan and Korea.  The difficulty was that no one knew how to tell these two scales apart.  And because the only place that the scale occurred was in the Dallas and Fort worth metroplex, it was difficult to interest others in investigating the problem without some financial backing.

After several years of slow spread through several north Texas counties, last year the scale made its move. In 2013 the scale appeared in several locations in Arkansas, Louisiana and Tennesee.  As a result, this winter researchers from the University of Arkansas and the USDA's Animal and Plant Health Inspection service agreed to lend a hand and take a closer look at these tiny insects.  

Molecular and new microscopic examinations now appear to confirm that our new scale is likely to be a recent import from Asia, probably Eriococcus lagerstroemia.  Last year Dr. Mengmeng Gu, Extension Horticulture specialist with Texas A&M AgriLife, had a chance to see these scales in their native Asian environment in a trip to China. The messy crape myrtles she saw there stimulated her interest in the scale, and led us to coauthor two new publications with the University of Arkansas. Both Texas and Arkansas now have fact sheets on this pest.
Crape myrtle branch with a heavy infestation of scale.

A scale-encrusted crape myrtle branch. Note
the pink blood from crushed scales where a
finger has been dragged across the infested
stem. Photo by M. Gu.
Many pest control professionals provide IPM services for landscape and turf pests, so it will be important to be able to recognize and identify it when you see it. Crape myrtle bark scale (CMBS) is a small white scale that bleeds pink when crushed. No other insects found on crape myrtle share these characters.  They can be found on the trunks branches and twigs of crape myrtle. Don't be surprised to find this scale in Arkansas, Louisiana, southern Oklahoma, Germantown, Tennessee, and possibly South Carolina. In Texas the Dallas/Fort Worth area is widely infested and it may also be found in Tyler, Longview, and College Station. Based on the current rapid spread, within the next ten years this scale will likely be common in many communities throughout the South.

If you are interested in learning more about CMBS, Dr. Gu asked me to talk about this pest this week in a Webinar, which is now posted on YouTube. In the webinar I discuss the appearance and damage caused by CMBS, how it is spread, and what is known about control.

The best control methods that we currently have involve soil injections of neonictinoid insecticides. Control recommendations are also listed here and in the fact sheets mentioned above. If you encounter this scale in areas outside Texas, or in areas of Texas I did not list, I would be interested in knowing about it. Leave comment on this site or drop me an email.  We hope to eventually have a website where sightings can be more easily reported.

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