Identifying and Treating Wood-Boring Beetles on Crape Myrtle

A Georgia homeowner noticed their two-year-old crape myrtle was struggling to leaf out in spring after a February pruning. Thread-like growths emerged from the bark, leaving tiny holes when brushed away, and a thin layer of moss had begun to coat the trunk. Initial insecticide sprays proved ineffective.

Entomologist Jack DeAngelis initially suspected a fungal issue but revised the diagnosis after reviewing a photo. The "threads" were actually compacted sawdust (frass) being expelled by wood-boring beetle larvae tunneling beneath the bark. The moss growth signaled the tree's vigor was already compromised.

Understanding the Pest

Wood-boring beetles lay eggs in bark crevices. Upon hatching, larvae bore into the wood, creating galleries that weaken the tree structurally and disrupt nutrient flow. The expelled frass often resembles sawdust but can clump into thread-like strands in humid conditions.

Treatment Options

• Systemic insecticides: Products containing imidacloprid (e.g., Bayer Advanced Tree & Shrub) can be applied as a soil drench. The chemical moves into the tree's vascular system, targeting larvae feeding inside. Success varies, and retreatment may be needed.
• Trunk sprays: Contact insecticides labeled for wood borers (often pyrethroids like bifenthrin or permethrin) applied to the bark can prevent new egg-laying. Timing is critical—apply when adults are active, typically late spring through summer.
• Cultural care: Reduce stress by watering during drought, mulching properly (avoid piling against trunk), and fertilizing based on soil test results. Healthy trees resist borers better.

When to Call a Professional

If the infestation is extensive, the tree is large, or structural stability is a concern, consult a certified arborist. They can assess whether the tree can be saved or if removal is safer.