Emerald ash borer (EAB) is a non-native, invasive, insect that kills ash trees. The grub or worm-like larvae of the borers spend the early stages of their lives beneath the bark, disrupting the movement of water and nutrients throughout the tree.  Eventually, this kills the tree.  The adults are small, iridescent green beetles that live outside of trees during the summer months.  The adult beetles fly to an adjacent uninfested ash tree, lay eggs on the bark infesting the new tree.  See the link for a brief video of the life cycle and destruction caused by the borer.

Indicators of infestation include crown thinning and dieback, bark splits that reveal “S” shaped galleries, increasing evidence of woodpecker activity on the tree and “D” shaped larval emergence holes.  Initially, the tree will respond by attempting to compartmentalize and seal bark splits, depleting energy reserves, and stressing the tree further.  Eventually, as the infestation advances, complete girdling of the trees vascular system occurs.  Unfortunately, because of the way EAB larvae feed underneath the bark, most symptoms do not become visible until infestation reaches significant levels.  Once symptoms become evident, trees decline rapidly.  

Anyone who suspects their ash tree(s) may be infested with emerald ash borer are encouraged to call Eagan Forestry at (651) 675-5300 or email the This email address is being protected from spambots. You need JavaScript enabled to view it..

How to identify an ash tree

Opposite Branching

Compound Leaves

5 to Many Leaflets















Common EAB symptoms:

  • Woodpeckers holes (woodpeckers are looking for larvae under the bark)
  • Sparse foliage ("canopy dieback") during spring and early summer
  • Splitting or cracking of bark
  • S-shaped or serpentine insect galleries in the bark
  • D-shaped exit holes on the tree trunk and branches

For more information, visit the Minnesota Department of Agriculture website and download their Does My Tree Have Emerald Ash Borer? guide.