Ash borer

Inspect ash and mountain ash trees for small emergence holes in bark, often with fine sawdust accumulating at base. Beneath bark you will find winding galleries packed with frass following the cambial layer. Look for branch dieback progressing downward and bark damage on sun-exposed trunks, particularly on stressed trees.

Maintain tree vigor through proper watering and mulching; borers attack weakened trees. Prune heavily infested branches during winter dormancy when borers are inactive. For valuable specimens, preventive trunk sprays of permethrin in late May to early June protect newly emerged adults. Once galleries establish inside wood, no spray kills larvae effectively.