Black silhouette of a tree with leaves on a white background.

Understanding Tree Borers and How to Stop Them

February 10, 2026

Tree borers are one of the most damaging pests affecting trees in Napa Valley. These insects tunnel beneath the bark, disrupting the tree’s ability to transport water and nutrients. Left untreated, borer infestations can weaken trees, increase safety risks, and eventually lead to tree death.



At Mike’s Tree Service, our certified arborists help homeowners identify borer activity early and implement effective treatment plans to protect long-term tree health.

What Are Tree Borers?

Tree borers are insects whose larvae feed inside tree trunks, branches, or roots. Common types include beetle larvae and moth larvae that burrow into wood as they develop.



Because borers live beneath the bark, damage often goes unnoticed until symptoms become severe.

Why Tree Borers Are a Serious Problem

Borers damage trees by:


  • Interrupting the flow of nutrients and water


  • Weakening branch and trunk structure


  • Creating entry points for disease and decay


  • Increasing the likelihood of limb failure


Over time, even healthy-looking trees can decline rapidly when infestations aren’t addressed.

Signs Your Tree May Have Borers

Homeowners should watch for:


  • Small holes in the bark


  • Sawdust-like material at the base of the tree


  • Oozing sap or resin


  • Thinning canopy or sudden branch dieback



  • Woodpecker activity targeting the trunk


If any of these signs appear, a professional inspection is recommended.

Why Borers Target Stressed Trees

Borers are attracted to trees already under stress from:


  • Drought or poor irrigation


  • Soil compaction


  • Improper pruning



  • Disease or root damage


Maintaining tree health is one of the most effective ways to reduce borer risk.

How Arborists Stop and Prevent Tree Borers

Professional borer management may include:


  • Tree health assessments


  • Targeted pruning of affected limbs


  • Soil and nutrient management


  • Preventative treatments when appropriate


  • Monitoring for reinfestation


Treatment plans are customized based on tree species, infestation level, and seasonal timing.

Why DIY Treatments Often Fail

Over-the-counter sprays rarely reach borers living beneath the bark. Incorrect timing or product use can stress trees further without addressing the infestation.


Certified arborists understand pest life cycles and apply treatments safely and effectively.

Final Thoughts

Construction equipment on a brown field under a clear blue sky, with a red pickup truck and a white jeep.

Tree borers can cause serious damage if left untreated, but early detection and professional care make a significant difference. Healthy trees are far more resistant to pests and environmental stress.


If you suspect borer activity or want a preventative evaluation, a professional inspection can help protect your trees and your property.

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