Crape myrtles remain a Louisiana favorite

Richard Bogren, Gill, Daniel J.

For Release On Or After 06/13/14

By Dan Gill
LSU AgCenter Horticulturist

Although native to the Far East, crape myrtles 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.

During the long blooming season, however, old flowers drop out of the trees constantly. This is a nuisance when trees are planted near patios, pools and where cars are parked regularly. Keep this in mind when deciding where to plant them in your landscape.

Crape myrtles are often planted at the corners of the front of a house to frame it. If you do that, make sure you locate them at least 8 to 10 feet away to accommodate their growth and eventual size.

A common problem with crape myrtles is the careless use of mowers and string trimmers around the base of these thin-barked trees. This type of equipment can easily damage the base of the trunk, leading to sickly, stunted trees. To prevent this type of damage, do not allow grass to grow within a foot of the trunk. To deter weeds, keep the area mulched with about 4 inches of pine straw pulled back slightly from the trunk.

To maintain a pleasing tree shape, regularly remove shoots – called suckers – that grow up from the base of the trunk. Prune them all the way back to their point of origin at the trunk or root. Make a flush cut, and don’t 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 areas with a product such as Monterey Sucker Stopper or Ferti-lome Sprout Inhibitor. Some local nurseries may carry these, or you can order them online.

A few insects and diseases attack crape myrtles, but they generally don’t cause significant damage. Common problems are crape myrtle aphids, powdery mildew and Cercospora leaf spot. Caterpillars also are an occasional problem.

Crape myrtle aphids are common, but control is really necessary only when populations are high year-to-year. The aphids excrete a sugary liquid called honeydew, which accumulates on the leaves and branches, and a black fungus called sooty mold grows on it. 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, such as permethrin. A light, paraffinic oil, such as Year Round Spray Oil and other brands, is your least toxic option. It can be used in summer and will help dislodge the sooty mold as well as kill the aphids. It will take repeated applications, however, as aphid populations return.

If don’t want to spray, you can control the aphids by drenching the base of the tree with the systemic insecticide imidacloprid. Check with the staff at your local nursery for the brands they carry. It is best 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.

Powdery mildew is a common disease in early summer during hot, dry weather. 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. Chlorothalonil can be applied in situations where the damage warrants treatment.

Cercospora leaf spot is a fungus disease that occurs more in mid- to late summer, particularly when weather is rainy. Dark spots show up on the leaves, which then turn yellow or orange and drop. Even though trees may lose a large portion of their leaves, there are no long-term, serious health effects. Spraying when you see the disease is not effective. By the time you see this disease, infection has occurred, and it’s too late to spray for it.

Cercospora leaf spot is not life-threatening and does not significantly affect the overall, long-term health of the trees. It is not practical to spray, and there is no need to do so.

Lack of flowers is a complaint I hear occasionally. Common reasons for lack of blooms include young trees, trees getting too much shade, trees that are sickly or low in vigor, and heavy insect or disease problems. Given time, good care and proper growing conditions, crape myrtle flowers are as certain as summer.

When it comes to choosing which crape myrtle to plant, it’s not just a matter of selecting a particular color. The desired mature size is also a very important consideration.

Crape myrtles are available in a range of sizes – from 10 to 12 feet to 25 to 30 feet tall. If you need a smaller crape myrtle, choose a smaller variety. If you want a white-flowering crape myrtle, for instance, you may plant an Acoma that grows to be 10 to 12 feet tall or a Natchez that grows to be 25 to 30 feet tall. Which size is best for the location where it will be planted? That’s up to you and the situation. But think about it and choose appropriately.

The top eight

Evaluated for growth habit, blooming, disease resistance and overall performance, these varieties have proven to be among the very best crape myrtles for Louisiana landscapes based on LSU AgCenter research trials – Acoma, 10 to 14 feet, white; Basham’s Party Pink, 25 to 30 feet, lavender pink; Muscogee, 25 feet, light lavender; Natchez, 30 feet, white; Sioux, 10 to 15 feet, vivid pink; Tonto, 12 to 14 feet, deep red; Tuscarora, 25 feet, coral pink; Tuskegee, 15 to 20 feet, dark pink.

Rick Bogren

6/2/2014 8:58:04 PM
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