Insects That Attack Crape Myrtle Trees
Crape myrtles (Lagerstroemia spp.) are small warm-season trees or shrubs that thrive in hot climates and dry soil. The crape myrtle, hardy in U.S. Department of Agriculture zones 6 through 9, offers exquisite pops of white, lavender, pink and red-colored blooms over one of the longest bloom periods of any tree, an average of 60 days. Once established, it is a low-maintenance and drought-tolerant tree, troubled occasionally by crepe myrtle pests.
Look for Crape Myrtle Aphids
According to the University of California Statewide Integrated Pest Management Program, one of the most common crape myrtle pests, the crape myrtle aphid (Tinocallis kahawaluokalani Kirkaldy) harms the crape myrtle in two ways. It feeds on the leaves causing yellow spots and deformed leaves, stunts the new growth of the tree and damages buds and flowers. The aphid also damages the crape myrtle by secreting honeydew, a waste from the aphid containing sugars that encourage the growth of sooty mold.
Sooty mold coats the leaves, reducing the tree's ability to make food. A natural cure for crape myrtle aphid is to introduce ladybugs, one of the aphid's natural enemies. If the infestation is too large, spray the tree with neem oil. Always read the product label for application rates, as instructions vary by brand.
Watch for Spider Mites
Spider mites (Tetranychidae) are hard-to-see little insects, most easily identified by the tiny webs, yellow dotted leaves and twisted foliage they leave behind. Severe spider mite infestations can weaken crape myrtles, leaving them susceptible to other diseases such as powdery mildew or black sooty mold.
The University of California Statewide Integrated Pest Management Program says to try washing the plants with a forceful stream of water, such as that from the hose, aimed at the undersides of leaves in the middle of the day. If this method does not work, safely apply neem oil at the rate indicated on the product label in early morning before the heat of the day, says the National Pesticide Information Center. Reapply the neem oil for crepe myrtle as necessary. Check the label before applying, as instructions may vary.
Keep and Eye for Scale
Scale (Eriococcidae) suck the saps out of the tree, causing stress and secretions from black sooty mold buildup, which also harms the tree. When looking for scale, check the bark and back side of limbs for slightly hairy looking, small white bugs that hardly move, instructs The Crape Myrtle Trails of McKinney. Ladybugs are a natural predator of scale and can be used to control small populations. For large infestations, use insecticidal soap applied to the trunk and reachable limbs with a soft brush to remove eggs, adults and the black sooty mold buildup and then treat with an insecticide.
Scale has a wax coat that makes spraying ineffective; instead, the most effective chemical treatment for scale is a water-soluble systemic insecticide drench, containing the active ingredient imidacloprid. The tree absorbs the systemic and kills the insects when bitten.
Carefully, mix imidacloprid with water per inch of circumference of the tree trunk according to the label directions. Pour the mixture around the base of the tree, taking care not to allow runoff into surrounding water sources. Read the brand's label before applying because instructions do vary.
Prevention of Crepe Myrtle Pests
Most of the insect problems in crape myrtles are preventable with proper planting and maintenance. The trees prefer eight hours of full sun a day and plenty of air circulation. Avoid planting crape myrtles in overly wet locations and avoid getting moisture into the branches and leaves, which creates habitats for insects to thrive.
Try to plant varieties that are resistant to diseases, such as powdery mildew, and insects. Prune crisscrossing branches to create better air circulation for the interior of the tree and prevents rubbing which can open up wounds for diseases and insects to enter the tree.