Maple Wound Decay: Managing Borers, Filling Cavities, and Long-Term Health

A Chicago-area maple lost a major limb 3 years ago. Wood chips now appear at the base; the wound is a hole. Homeowner plans Merit insecticide and expandable foam.

Understanding the Decay Process

Decay fungi enter through wounds, digesting dead heartwood. The living cambium (just under bark) remains functional. A hollow tree can thrive for decades if the cambial ring is intact. First sign of structural concern: hollow limbs breaking in storms.

Recommended Actions

• Borers: Spray Merit (imidacloprid) on wound edges in spring. Systemic soil drench (Bayer Advanced) gives season-long protection.
• Foam filling: Cosmetic only. Use low-expansion foam; stop flush with bark. Does not stop internal decay.
• Health maintenance: Annual 10-10-10 at 1 lb/inch trunk diameter (spring). Mulch 3 inches to drip line. Deep water (1 inch) weekly in drought.

What NOT to Do

• Don't use concrete, tar, or wound dressings—they trap moisture, accelerate decay.
• Don't seal squirrels inside—evict first (one-way door), then foam.

Monitoring

Annual inspection for: new frass, expanding cavity, canopy thinning, limb dieback. Consult an ISA-certified arborist every 2–3 years for risk assessment.

With good care, this maple can remain a safe, beautiful shade tree for many years despite the cavity.