Crape Myrtle: How to Protect your Apartment’s Landscape
A colorful staple of southern apartment landscapes has come under attack in recent years. And agricultural and landscape professionals are a little stumped about how it originated or finding ways to quickly fend advances.
Crape Myrtle bark scale, or Eriococcus lagerstroemia, is slowly advancing since its U.S. discovery in Dallas about 12 years ago. In the last few years, the pest has been seen in Oklahoma, Louisiana, Alabama and Tennessee. Some say damage could severely impact Crape Myrtle production, use and marketability.
The tiny hard-shelled insect, believed to have originated in Japan or China, is responsible for slowing the growth and beauty of one of the most popular attractions of residential and commercial landscapes. Crape Myrtles have been grown in the U.S. for more than 150 years and are popular for their colorful and long lasting flowers. According to the University of Florida, almost three million Crape Myrtles worth more than $42.8 million were domestically produced in the U.S. in 2013.
“The potential for spreading throughout the country is there,” says Tod Russell, an insect specialist at Earthworks. “Scale attacks throughout the year. When you see it spring up, it’s a matter of time before they inundate the plant.”
Bark scale can stunt growth and affect Crape Myrtles appearance
Crape Myrtle bark scale, which is similar to Azalea bark scale, starts on branches and branch tips and leaves behind a sticky, shiny substance similar to what Aphids excrete on leaves. An early sign of a scale infestation is a black, mold-like coating on the bark and branches.
The insects are white and usually congregate near pruning wounds or branch crotches. Once they’ve infested, the bark looks ragged and bloom growth is stunted. A fully blossomed and colorful piece of the landscape will begin looking sickly.
Fortunately, the ruggedness of Crape Myrtles is limiting scale damage to only an unhealthy appearance. The insects have not been known to kill the plants, which are known for their durability and being a safe landscaping bet.
Systemic treatment takes time but is effective
However, the pest control industry has struggled over the years to find a fast, effective treatment once the damage starts. Russell says the best recommendations for treatment are as simple as washing the trunk and reachable limbs with mild soapy water or applying an insecticide at the roots to slow and eventually eliminate scale advancement.
Because scale insects have a hard shell, spray insecticides and traditional horticultural oils are only partially effective. The shell creates an impermeable barrier to help the insect avoid contact with sprays.
A systemic treatment of applying a neonicotinoid insecticide near the Crape Myrtle’s roots has proven a better option, Russell says. The roots absorb and distribute the chemical throughout the plant, and insects ingest it when they feed. But the results are slow.
Periodically inspect Crape Myrtles for insect infestations
Russell says apartments should make periodic inspections of Crape Myrtles to look for signs of the scale. Most infestations are usually noticeable by early summer when they begin to multiply as plants are taking in moisture and nutrients they need to survive and thrive. However, it doesn’t hurt to check year-round, especially during warmer weather.
Once an infestation is noticed, treatment should be considered. Treating is best May through July, but can still be effective at other times. Treatment results can take as long three or four weeks to kill the scale, and can last as long as one to three years depending on the surrounding insect pressure.
“When the plant is taking in the most the fastest, that’s when you get the best control,” Russell said. “My experience is they just don’t fall off when you treat. It can take six months to a year for it to fall off.”