Large White Grubs in Maple Trunks: Flatheaded Borers

Thumb-sized white grubs found in rotten areas of 50-year-old maples being removed in Nebraska. Owner wonders if grubs cause rot or exploit it.

Identity

Likely flatheaded borers (e.g., sugar maple borer, Glycobius speciosus). Adults lay eggs in bark cracks; larvae mine cambium and sapwood, expanding decay.

Relationship to Decay

Borers enter existing wounds/decay; they don't initiate it but accelerate structural degradation. Their galleries invite wood-decay fungi.

Control (for standing trees)

• Trunk spray with imidacloprid (Merit) or other labeled borer insecticides.
• Timing: early summer for egg-laying adults.
• Cultural: keep trees vigorous; avoid wounds.

In already-removed trees, no action needed.