Gardening for the Record: Protect crape myrtles; bark scale is back in town – Times Record

By Lucy Fry

Crapemyrtles are unquestionably the most popular ornamental trees in the Southern landscape, offering something for every season colorful flowers in summer, brilliant foliage in autumn and interesting brown exfoliating bark in winter.

And they cope with Mother Natures heat indexes of 110 and drought conditions by producing huge fragrant panicles of crinkled white, pink, red and lavender flowers.

A drive around town reveals how much Fort Smith loves its crape myrtles. They are everywhere in parks, along highways, in small yards and large estate landscapes, on campuses and in front of businesses.

But lurking behind this beautiful summer display is a threat its called crape myrtle bark scale. It begins as tiny white or gray felt-like encrustations on small twigs and even large trunks often near pruning wounds or in branch crotches on older wood. Then it gives off sticky honeydew and finally turns into a black sooty mold on the bark. (Although it is sometimes mistaken for a severe aphid problem, it is not.)

This insect arrived in Arkansas via Texas and last year invaded the river valley with a vengeance that many crape myrtle growers remember all too well.

Several neighbors and friends have already spotted it this year and are considering topping their trees so that they can reach and clean the nasty little scale. This sounded so desperate that an imminent email to Plant Doctor Sherrie Smith (her real title is University of Arkansas plant diagnostician) was necessary for any new recommendations or remedies for controlling this pest.

As expected, she replied immediately: We have not added anything new. If the grower uses one of the systemic insecticides recommended, there is no need to top the crape myrtle.

Here are the UA Cooperative Extension Services recommendations:

It does not appear that crape myrtle bark scale will be easy to control, though soil-applied neo-nicotinoids do provide significant suppression. Our current best suggestions for control 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. Be sure to use sufficient volume to allow for penetration behind loose bark and into cracks and crevices. 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 has shown the most promise in tests to date. Imidacloprid (Merit or Bayer Advanced Garden Tree and Shrub Insect Control), thiomethoxam (Meridian) and dinotefuran (Greenlight Tree and Shrub Insect Control with Safari) have shown best control when applied between May and July. When drenching the soil with a systemic insecticide, allow several weeks for the product to be distributed throughout the plant. Additionally, acetamiprid and clothianidin, also neonicotinoids, have demonstrated good control.

Lady beetles should be preserved, as the twice-stabbed lady beetle is an efficient predator of this scale.

Twice-stabbed lady beetles (black with two red spots on their backs) are a gardeners friend thanks to their ability to hunt and consume plant-harming bugs, primarily scales, at an astonishing rate.

If fact, your garden will benefit from plants that attract friendly beetles and ladybugs that consume aphids with a vengeance. These plants include dill, cilantro, wild carrot, angelica, cosmos, yarrow, geranium and (most gardeners will hesitate before using this one) dandelions.

So, to all you desperate crape myrtle fans: Leave your chainsaw in the garage, pull on your gloves, scrub and treat your trees and pray for an invasion of the twice-stabbed lady beetle.

Next week, the topic will be: saving the pollinators one stamp or one plant at a time.

Lucy Fry of Fort Smith is a level 4 Master Gardener and writes the area Master Gardener newsletter. Her column, Gardening for the Record, runs weekly in the Times Record. Send questions to gardeningfortherecord@gmail.com.

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Gardening for the Record: Protect crape myrtles; bark scale is back in town - Times Record