Although native to eastern Asia, crape myrtles (Lagerstroemia) are almost indispensable in the Southern landscape. Their vibrantly colored flowers in shades of pink, purple, red and white from May to September virtually define the summer season here. The relatively small size of crape myrtle trees and long, colorful blooming season make them useful in a variety of landscape situations.
With proper care, crape myrtles can remain healthy and attractive for decades. Problems arise occasionally, however, that do require some attention and care.
Don't bite the bark
A common problem is the careless use of mowers and string trimmers around the base of these thin-barked trees. To prevent this type of damage, do not allow grass to grow within a foot of the trunk. Keep the area with about 4 inches of mulch pulled back slightly from the trunk.
Crape myrtle trees occasionally shed their outer layer of bark. We are seeing this a lot this year. This is natural and no need for concern. Shedding the outer bark often reveals different shades and colors from tan to rusty brown, which adds to the beauty of these trees.
A sucker's born every minute
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Most crape myrtle trees will send up lots of shoots from the base, especially when they are younger and growing rapidly. To maintain a pleasing tree shape, regularly remove these shoots — called suckers — from the base of the trunk.
Remove suckers as soon as they appear. They are easier to deal with and cause less damage to the tree when they are removed early. Prune them all the way back to their point of origin at the trunk or a root. Do not leave a stub or several suckers will appear for every one you cut off.
To prevent suckers from growing back so fast, treat the freshly cut spots with a product such as Monterey Sucker Stopper or Bonide Sucker Punch (some nurseries and feed stores may carry these, or you can order online).
Pests
A few insects and diseases attack crape myrtles, but they generally don’t cause significant damage. Common problems are crape myrtle aphids, crape myrtle bark scale, powdery mildew and Cercospora leaf spot. Caterpillars are an occasional problem, including stinging types like the IO moth and saddleback caterpillars.
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Crape myrtle aphids are common and most trees get them during summer. Only when populations are high every year is control really necessary. The aphids feed on the sap and excrete tiny droplets of a sugary liquid called honeydew. This accumulates on the leaves and branches and causes the growth of a black fungus called sooty mold. Heavy infestations of aphids can lead to so much sooty mold as to turn the tree almost all black.
You can control aphids by spraying the tree with any commercially available insecticide labeled to control aphids. A light, paraffinic oil, such as Year Round Spray Oil or All Seasons Oil, is your least toxic option. It can be used now and will help dislodge the sooty mold as well as kill the aphids.
If don’t want to spray, you can control the aphids by drenching the base of the tree with a systemic insecticide. Systemic insecticides, such as Bayer Advanced Tree and Shrub Insect Control, are absorbed by the tree’s roots and then move internally throughout the plant. It is better to apply a systemic insecticide early in the season, around April or May, but you should get some late-summer benefit if you apply one now. This will also help control bark scale.
Two diseases, powdery mildew and Cercospora leaf spot, are occasional problems. Powdery mildew is a minor problem that usually attacks vigorous new growth. It appears as a white, powdery coating or spots on leaves and flower buds. Treatment is rarely needed, although heavy infections of the flower buds can cause them to abort.
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Cercospora leaf spot occurs in summer, particularly when weather is rainy. Due to all the rain, this disease is common now. Dark spots show up on foliage that then turns yellow or orange and drops. Although this disease can be debilitating if it causes repeated leaf drop, control is not generally needed. This disease will not kill a tree and control is generally not practical — by the time you see the symptoms, it is too late to control the outbreak.
Bouquet buffet
Although crape myrtle trees are shapely and have beautiful, muscular trunks and attractive bark, it is the flowers that we really enjoy. Did you know that crape myrtles make great cut flowers? Harvest flower clusters for vases indoors where you can enjoy them in bouquets alone or combined with other summer flowers.
This can be helpful when young trees produce long, vigorous shoots with a large flower head at the end. The weight of the flowers, particularly after rain, can significantly bend down these branches. To relieve the weight, cut off the flower head and put it in a vase inside. The branch will spring back upright once the flowers are cut.
Lack of flowers is a complaint I hear occasionally. Common reasons for lack of blooms are: young trees, trees getting too much shade, trees that are sickly or low in vigor (try fertilizing in the spring) and heavy insect or disease problems. Given time, good care and proper growing conditions, however, crape myrtle flowers are as certain as summer.
