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Wood Borer Treatment and Cavity Management in Large Tree

Dealing with Borers, Decay, and a Squirrel Tenant

A Connecticut homeowner has a large tree (>100" circumference) with a deep cavity, wood borers, decay fungi, and a resident squirrel. Previous advice: Merit (imidacloprid) for borers.

Merit Application Clarification

Formulation: Liquid concentrate mixed with water = spray solution
Application: Spray trunk/bark around cavity entrance, not into cavity
Timing: Spring/early summer when borers active
Label compliance: Follow manufacturer directions; soil drench may be alternative

Cavity and Squirrel Management

Evict squirrel first (wait for it to leave)
Insert chicken wire or hardware cloth as foam backer
Fill with expanding closed-cell foam flush with bark
Do not overfill – foam should not protrude

The squirrel's nesting actually cleans the cavity to sound wood, reducing borer habitat. If squirrel remains, it deters borers but maintains entry hole.

Decay Fungi Reality

Decay is in dead heartwood; living tissue is outer sapwood
No treatment stops internal decay
Fertilize (10-10-10 at 1 lb/inch trunk diameter) to boost vigor
Monitor for limb failure risk as decay spreads upward

Professional Assessment Strongly Recommended

Contact Connecticut DEEP Forestry for free forester visit. A tree this size with cavity, decay, and borers needs hands-on evaluation for structural risk.

Trees: Bradford Pear Borers: Sawdust, Dying Leaves, and How to Save the Tree; Crepe Myrtle Borers in Georgia: Contact Extension for Spray Timing; Saving a Redbud Tree from Wood Borer Infestation; Burning Mimosa Wood: Seasoning Time for Best Results; Creosote Buildup: Caused by Unseasoned Wood, Not Species; Transplanting Large Maple Trees: Hole Preparation, Timing, and Clay Soil Solutions; Holes in Tree Trunk: Woodpecker or Squirrel Nest; Borers in Eucalyptus and Valley Oak: Likely Longhorn Beetles; Borers in Cut Eucalyptus Firewood: Solarize or Split to Save the Wood; Sapsucker Holes in Live Oak: Not Borers, But Birds

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