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Oklahoma County Cooperative Extension Service

Lessons from the Garden: The New Crape Myrtle Malady

OSU Extension Center

Ann Larson, Oklahoma County Extension Master Gardener

2500 NE 63rd Street

OKC, OK  73111

405-713-1125

5-15-2018

 

 

Lessons from the Garden: The New Crape Myrtle Malady

 

 

My crape myrtles look like they have a bad case of dandruff.  The beautiful maple-colored trunk of my huge Natchez favorite is covered in little white spots and a black, sooty mold.  The bark on my Burgandy Cotton is similarly spotted and marred.

 

I’ve come to discover it’s a new, exotic pest, Crape Myrtle Bark Scale (CMBS) that has only recently begun invading Oklahoma.

 

This disease came to the U.S. from Asia in 2004, arriving first in Richardson TX, on nursery stock.  It has only begun appearing in Oklahoma in the last couple of years.

 

It is disheartening to watch beloved plants in such condition.  In my time as a gardener, I have witnessed the onslaught of pine wilt disease, which took out tall, stately pines, many in my neighborhood.  Rose rosette disease claimed all my Knock-out roses, those “foolproof, easy to grow” bushes that gave us endless pleasure…until they didn’t.  I recently lost two Shumard oaks to Hypoxylon canker.  And now this.

 

Luckily CMBS is not fatal, or so that’s what I’ve gleaned from Extension Service sources both here and in other nearby states, and I am clinging to that belief.  Nonetheless, it was shocking to discover in my own backyard.

 

I have had a long love affair with crape myrtles (Lagerstroemia indica), beginning as a child when I would decorate my tea party plates with the lovely watermelon-red blooms from my parents’ large shrubs.

 

The crape myrtle was one plant they grew to appreciate, probably because, having grown up in Nebraska and Wyoming and with five small children in tow in Oklahoma City, they didn’t have much time to figure out our state’s quirky conditions. 

 

Crape myrtles were the perfect landscape solution for them:  totally adaptable to Oklahoma’s heat and humidity, it’s drought, its wind (although swimming pool owners might disagree).  They flourish in just about any soil and thrive on neglect and still grow quickly and produce beautiful blooms all summer long. Their only real problem, until now, has been powdery mildew.

 

But even that has been reduced over the years by the development of new cultivars, beginning as far back as the 1950s at the U.S. National Arboretum, which has a long-term crape myrtle breeding program. 

 

Their cultivars (the first L. indica and Lagerstroemia fauriei cross), which are not prone to powdery mildew, are all given Native American names, such as Muskogee and Hopi, Arapaho, Cherokee and Osage, to name a few. 

 

In the mid-1990s, Dr. Carl Whitcomb introduced new cultivars such as Dynamite and Red Rocket with true red flowers.  More recently Dr. Cecil Pounders began breeding the dramatic black-leafed varieties; and in 2015, the Enduring Summer series was released, many of which are reblooming. The choices are mind-boggling and hard to resist.

 

Crape myrtles are one of the most popular woody ornamental flowering shrubs/small trees in the Southeast, and it is no wonder.  They are the stars of my summer garden, just as they were in my earliest garden recollections.

 

Their colorful blooms are audacious.  Their bark can be equally as stunning.  When other plants wilt in our brutal summers, these showy shrubs (or small trees) take the heat and humidity in stride.  It’s almost as if they’re just waiting for their competition to fade and fizzle before they take their place on the landscape stage.

 

And they often don’t take their curtain call until after their brilliant autumn leaves fall, making it by far one of Oklahoma’s best blasts of color, and definitely one of the best garden bets for your bucks.

 

But now many of those beauties are covered in spots, little white spots that squirt pink liquid if you squish them

 

So far this disease is only affecting crape myrtles (although there are some reports it is affecting American beautyberry, too), and treating this disease is tricky.   Extension experts say it is difficult to control without the use of systemic insecticides, but the active ingredients pose a risk to pollinators, so, for now, they are discouraging the use of these products.

Instead, they suggest scrubbing the infested bark with a soft brush and a mild solution of dishwashing soap and water, which will remove many of the female scales and egg masses as well as buildup of black sooty mold on branches and trunks.  

Horticulture oil, they say, may be effective when applied during the winter at a dormant application rate.  To ensure adequate coverage of the entire tree, they recommend using enough oil to reach behind loose bark, branch crotches, and other crevices.

And if you’re in the market for a crape myrtle, be sure to examine it carefully before purchasing. 

In the meantime, my fingers are crossed that those brilliant horticulturists are working right now to find predators to provide natural control of this pest, along with developing new cultivars that will be resistant to this disease.  But for now, my yard is full of crape myrtles that all need a bath.

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