Saving Sugar Maples from Borer Damage

Treating Borers in Transplanted Maples

Nine-year-old sugar maples showing dieback, early leaf color, and a hollow trunk with a bore hole at eye level are classic signs of borer infestation—likely flatheaded or roundheaded borers attacking stressed trees.

Immediate Treatment

• Insecticide: Spray trunk and major limbs with Merit (imidacloprid) or a labeled borer spray. This kills larvae inside and prevents new attacks.
• Fertilize: Broadcast 10-10-10 fertilizer around the drip line and water deeply to stimulate root growth.
• Mulch: Apply 3 inches of organic mulch (wood chips, shredded bark) in a wide ring—keep it off the trunk to prevent rot.

Why This Works

Borers target trees under stress (transplant shock, drought, poor soil). Improving vigor helps the tree compartmentalize damage and resist future invasions. Merit is systemic, moving into the cambium where borers feed.

Where to Find Products

Local nurseries and garden centers carry borer sprays and tree fertilizers. Ask for “borer control for ornamental trees.”

Monitoring

Inspect trunks monthly for new holes, frass (sawdust), or dieback. Early retreatments may be needed for 1–2 seasons.