Managing Borers in a Mature Japanese Maple

A 30-year-old Japanese maple in Victoria, Australia shows bark lifting and a dead limb—classic signs of borer infestation. Once borers tunnel inside, they're nearly impossible to kill with contact sprays.

Systemic Treatment Option

The best approach is a soil-applied systemic insecticide containing imidacloprid (e.g., Bayer Tree & Shrub Insect Control). Applied as a drench, the tree transports it to the canopy where borers feed. Timing: apply in early spring as buds swell for optimal uptake.

Supporting Tree Health

• Water deeply during dry periods.
• Mulch 2–3 inches deep (keep away from trunk).
• Fertilize based on soil test results.
• Avoid wounding bark with mowers or trimmers.

When to Remove

If more than 30–40% of the canopy is dead, or the trunk has extensive bark loss, the tree may be a hazard. Consult a certified arborist for risk assessment.