Start caring for crape myrtles now

Richard C. Bogren, Owings, Allen D.

While some crape myrtle pruning cuts may appear “architecturally” nice, this kind of pruning is still the improper way to prune crape myrtle trees. (Photo by Allen Owings)

Immature crawlers of crape myrtle bark scale are active in early spring. (Photo by Mississippi State University horticulturist Gary Bachman, used with permission)

News Release Distributed 03/27/15

By Allen Owings

LSU AgCenter horticulturist

HAMMOND, La. – Our spring- and summer-flowering trees and shrubs are growing and preparing for another great bloom season. One of favorite landscape plants for late spring and summer is the popular and loved crape myrtle.

In order for blooming to be best this summer, spring management practices are important. We also need to watch for a new crape myrtle pest – crape myrtle bark scale.

For the best summer blooms, make sure your crape myrtle trees receive maximum sunlight – at least eight hours of direct sun a day. We recommend fertilizing crape myrtle trees in the late winter or early spring – mid-March to mid-April is ideal. You can use a slow-release fertilizer or you may select 8-8-8, 13-13-13 or similar balanced fertilizer formulations.

Watch new foliage in spring for aphid infestations. These insects feed on terminal growth and cause sooty mold to develop on leaves if populations are not controlled.

One of the main issues with crape myrtles now throughout Louisiana and problematic in other states, too, is the rapid upsurge in improper pruning techniques. We refer to this as “crape murder.”

Cutting back crape myrtles by reducing their height is not the correct way to prune. If a crape myrtle needs pruning, the best thing to do is to thin the interior stems of the plant canopy. Heading back the terminal branches by a foot or so is acceptable, but major heading back isn’t.

In addition to crape murder, proper management and aphids, we need to be aware of the relatively new invasive pest affecting crape myrtles in Louisiana. Crape myrtle bark scale is very serious. Trees with crape myrtle bark scale have fewer blooms.

Crape myrtle bark scale was first found in the United States in Texas in 2004 and is now in Oklahoma, Arkansas, Louisiana, Mississippi, Alabama, Florida, Tennessee and Georgia. They have been identified in Louisiana in the Shreveport-Bossier City area, Minden, Monroe, Rayville, Houma, Hammond, uptown New Orleans and possibly Alexandria. The immature insects start moving in midwinter in Louisiana, and populations build all through summer.

Crape myrtle bark scale will appear as white or gray encrusted waxy spots around pruning cuts and in the crotches of branches. Sometimes the insects exude a pinkish tinge or liquid when touched or squished. Black sooty mold covering stems and trunks rather than primarily on foliage when aphids or white fliers are present is a “drive by” way to observe possible scale populations.

Heavy infestations can be scrubbed with soap and water or pressure washed with a sprayer or garden hose to physically remove insects. A systemic insecticide is a treatment for long-term control to eliminate or reduce populations. Apply the insecticide to the plant in April; timing is critical. Systemic insecticides include dinotefuran (such as Greenlight Tree and Shrub Insect Control with Safari) and imidacloprid (such as Bayer Advanced Garden Tree and Shrub Insect Control). These products can lead to significant population reductions by midsummer.

Be observant in the landscape and scout for potential problems. It’s easier to control problems early on than to try to handle them by summer or fall.

You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.

Rick Bogren
3/27/2015 11:57:00 PM
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