THE CRAPE SCRAPE
Scale infestation in Crape Myrtles perplexing to tree professionals
Two years ago, a few Germantown residents began noticing an ugly and sticky black substance on their azaleas and other shrubs and perennials.
Their problem, they soon learned, was not supernatural curse or even a plant disease attacking their shrubs. It stemmed from infestations of scale insects on their crape myrtles that suck sap from the trees and then produce a sweet excretion known as “honeydew.”
As the honeydew falls from the tree onto nearby shrubs, it promotes the growth of sooty mold.
For tree professionals and tree appreciators, this was an alarming occurrence. They feared it might threaten the thousands of crape myrtles planted in front and backyards, public parks, medians and other commercial and municipal landscapes.
It’s difficult to imagine our summer landscapes without these long-blooming colorful flowers. And we probably don’t have to.
“The scales will stress the trees but not necessarily kill them,” said Dr. Chris Cooper, a Shelby County Extension agent. But, he added, other pests and diseases can move into a weak tree and hasten its demise.
Dr. Mark Follis, owner of Follis Tree Preservation, is also optimistic about the crapes after treating a badly infested tree in 2012 and 2013. He used a professional-strength product containing imidacloprid, which is also the key ingredient in products such as Merit and Bayer Advanced Garden Tree and Shrub Insect Control.
“Today that tree is absolutely clean,” said Follis, adding that he also provides a deep soil fertilizer for the trees he treats.
But he’s also seeing infestations of bark scales spread to trees in East Memphis, Midtown, Harbor Town and other parts of metro Memphis. Cooper said infested trees have been seen in Fayette County as well.
The long-term health of the trees is more difficult to predict because the problem is a new phenomenon first spotted in 2004 in Texas. Experts surmise the insects were brought to America on tree seedlings from Asia.
Until more research is completed, a lot remains unknown about the problem, including which crape myrtle cultivars are especially susceptible or resistant to the insect; how the insects move around since the females can’t fly and if the use of soil-drenching chemicals is a practical long-term solution.
The problem is perplexing even to experts like Cooper. Three of his four crape myrtles have no infestations; one did until he treated it last year.
“With just one or two chemicals to treat it, I’m concerned about what will happen when the scales develop resistance to them,” Follis said.
Nurserymen are concerned about protecting the U.S. crop, which has a wholesale value of about $46 million.
During his program last week at the Agricenter, Cooper recommended a way homeowners can treat trees with the scales, which appear as little white ovals on branches, crevices and under peeling bark.
First, wash off the insects and the sooty mold by using a pressure washer, pressure nozzle on a hose or a soft brush and water. Add a little (a few drops) dishwashing liquid or insecticidal soap to the wash water if possible.
Following the recommendations on the imidacloprid label, prepare a soil-drenching solution and pour it around the root zone of the tree as directed. Experts say the best times to do it is in May and June when crawlers emerge.
Follis said some new research indicates the treatment time isn’t that critical. He also thinks washing trunks before treatment is unnecessary except for cosmetic reasons.
It will take two to three weeks for the tree roots to absorb the insecticide and distribute it through its tissues. Spraying directly on the scales and on branches high in the tree is not recommended. The effectiveness of using dormant oils to suffocate eggs during the winter is unknown.
To keep crape myrtles strong and resistant to pests and diseases, do not pamper them with too much water, fertilizer or pruning. All of these errors lead to the proliferation of tender young shoots that are more susceptible to insect damage, Cooper said.
BECOME A MASTER
Applications for the next master gardener training program are available at offices of Shelby County Extension at the Agricenter and in downloadable form: memphisareamastergardeners.org
The 45-hour course will be offered on Wednesday mornings beginning in early January and continuing to mid-April. The fee is $150. In addition to successfully completing the course, master gardener “interns” must do 40 hours of volunteer work to graduate.
Applications must be submitted by July 31. Send no money with the application. Candidates will be interviewed by a master gardener before being admitted to the program.
WORK IT OUT
The Memphis Botanic Garden is offering a horticultural therapy workshop on July 9 and 10 aimed at service providers who want to use horticulture for therapeutic goals with special needs populations.
Participants receive an overview of horticultural therapy, accessibility and adaptations for special needs, horticultural and botanical craft ideas and information on how to start and implement a program. A $100 fee covers both days and includes lunch on Thursday. Call 901-6364128 for information.