I see tiny holes and sawdust piles at the base of my tree trunk. What's causing this?

Tiny holes with accumulations of fine sawdust (called frass) at the base of your tree indicate boring insect activity. This is a serious concern because wood-borers feed inside the trunk, disrupting the tree's vascular system and weakening its structural integrity.

Common culprits by hole characteristics:

• Round holes, 1/16 inch: Ambrosia beetles — they bore into stressed or recently transplanted trees and cultivate fungal gardens inside
• Round holes, 1/4 inch with coarse frass: Clearwing borers or roundheaded borers
• D-shaped holes, 1/8 inch: Emerald ash borer (if it's an ash tree — see our EAB Guide)
• Oval holes with very fine dust: Powderpost beetles (more common in dead wood/lumber)
• Large holes, 3/8 inch+: Asian longhorned beetle (a quarantine pest — report immediately to USDA at 1-866-702-9938)

Key diagnostic questions:

1. What species is the tree? Borers are often host-specific.
2. Is the tree stressed? Most borers target weakened trees. Drought, recent transplanting, construction damage, and soil compaction are common stressors.
3. Where on the trunk are the holes? Base, mid-trunk, and upper canopy borers are different species.

What to do:

1. Collect samples — save some frass and take photos of the holes with a coin for scale.
2. Have a certified arborist identify the pest before treating.
3. Systemic insecticide injections are effective for many borers if caught early.
4. Address underlying stress — proper watering and mulching are essential.

Learn more at Signs of Insect Damage on Trees.