Diagnosing and Treating Maple Tree Borers

"Apple tree maggot" is a misdiagnosis—these pests attack fruit, not Norway maples. Your tree likely has flatheaded appletree borers or other shade tree borers exploiting stressed tissue.

Borers: Secondary Invaders

Borers successfully attack only stressed or injured trees. Their 1-3 year development occurs under bark, with adults emerging to lay eggs on compromised hosts. Your mature maples' emergence holes indicate past infestation cycles.

Integrated Treatment Approach

1. Trunk spray: Imidacloprid (Merit) applied to bark penetrates to feeding galleries
2. Soil drench: Same product as systemic root uptake for ongoing protection
3. Vigor restoration: Fertilize with 10-10-10 at 1 lb per inch trunk diameter—fall and spring
4. Water management: Deep watering during drought reduces stress attraction

Critical Timing

Apply imidacloprid now for current larvae and again in spring for new hatch. Combine with fertilization to boost tree's natural defenses. Healthy maples resist borers through vigorous sap flow that drowns larvae.