Borers in Mature Maple Trees: Identification and Treatment Options

Recognizing Borer Infestation

A 65-year-old maple with wood shavings (frass) at the base and woodpecker activity is a classic sign of wood-boring insects—likely flatheaded borers (e.g., Chrysobothris spp.) or carpenterworms. These pests tunnel in the cambium and sapwood, disrupting vascular flow.

Why Borers Attack

Borers target stressed trees. Common stressors include:

• Mechanical damage (lawn mowers, string trimmers)
• Drought or compacted soil
• Improper pruning wounds
• Sunscald on thin-barked maples

Treatment Strategies

Chemical Control

• Systemic insecticides: Imidacloprid (Merit) as soil drench or trunk injection—absorbed into vascular tissue, kills feeding larvae.
• Bayer Advanced Tree & Shrub Insect Control (imidacloprid) applied to soil—easy, season-long protection.
• Trunk sprays: Permethrin or bifenthrin during adult flight (spring) to prevent egg-laying.

Cultural Prevention

• Mulch 3 inches deep to prevent mechanical injury.
• Water deeply during drought.
• Avoid wounding bark; prune properly in dormant season.
• Fertilize based on soil test to maintain vigor.

Organic Limitations

No reliable organic sprays kill borers inside the tree. Beneficial nematodes (Steinernema carpocapsae) may help if injected into active tunnels, but efficacy is variable.

Assessing Tree Survival

If canopy is still full and damage is localized, treatment can save the tree. Extensive girdling or >50% canopy dieback may warrant removal for safety.