Bringing a profusion of summer blossoms and vibrant fall foliage into the home garden, the crape myrtle bush's interest quickly wanes when pests attack. Crape myrtles, Lagerstroemia species, display green leaves that turn to vivid warm hues of yellow, orange and red during autumn. However, if your leaves appear yellow and are sticky to the touch when they should appear green and smooth, act quickly to prevent potential pest damage.
Preventive Care
Maintain optimal care of your crape myrtles as healthy bushes avoid and regain health from pest problems with greater ease than unhealthy bushes. Grow crape myrtle plants in parts of the home landscape that provide full sunlight for best development, flowering and vibrant color. Maintain moist, well-drained soil, though crape myrtles tolerate dry conditions once established. Keep soil pH at a range of 5.0 to 6.5. Prune crape myrtles when they are dormant to remove central branches to increase circulation. Also, remove dead and dying twigs but avoid topping and severe pruning that can injure your bush.
Problem
If leaves are yellow and sticky, your crape myrtle is likely infested with crape myrtle aphids, Tinocallis kahawaluokalani. These pests display light yellow-green bodies with black specks. Total body length measures approximately 1/16 inch. You will only see these pests on crape myrtle bushes as these aphids are host-specific and will not spread to plants of other species within the garden. Crape myrtle aphids typically appear from May through September with most activity occurring during July and August. Look for these pests primarily on the lower surfaces of leaves where they feed.
Damage
Aphids feed on crape myrtle leaves by piercing plant tissue with their mouths and sucking out tissue fluid. As they feed, they excrete a sticky, sugary substance called honeydew. Honeydew drips from crape myrtle aphids onto leaves and plant parts below, often saturating them, resulting in a sticky feel and a "varnished appearance," according to the North Carolina State University. Aphid feeding directly damages plants with the development of yellow spots on leaves. Twigs, flowers and leaves may not develop correctly while leaves display a distorted appearance without growing to full size. In addition, honeydew promotes the development of a fungus called sooty mold. A black hued fungus, sooty mold growth can cover leaves, blocking sunlight and disrupting necessary absorption.
Solution
To control crape myrtle aphids, release natural enemies onto your plants. Natural enemies are beneficial bugs that kill aphids without harming the crape myrtle bush. Purchase enemies like green lacewings and parasitic wasps from garden supply stores, catalogs or online. For severe infestations, apply a chemical control. Spray crape myrtles with insecticides with the active ingredient acetamiprid or thiamethoxam. Though these insecticides control aphids without wiping out natural enemies, a lower toxicity option includes botanical based horticultural oil. Horticultural oil kills aphids on contact and often requires reapplication for thorough management.
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