Across Edina and nearby Twin Cities suburbs, oak trees that seemed perfectly healthy in spring are now browning out, dropping branches and thinning at the top. City forestry staff say a native beetle, the two-lined chestnut borer, is driving the sudden summer decline and is hitting many mature oaks that had not shown obvious problems before this season.
Foresters say the beetle is acting as a secondary attacker, moving into oaks that were already stressed by drought and other pressures. According to the Minnesota DNR, severe droughts from 2021 to 2023 primed large swaths of oaks for decline. The two-lined chestnut borer's larvae feed in the inner bark and cambium of those weakened trees and often kill them within two to three years.
How to spot the beetle
Homeowners are being told to watch for canopy dieback that starts at the top of the tree and works its way downward, along with wilting or yellowing leaves in mid-summer and small D-shaped exit holes in the bark. The University of Minnesota Extension notes that sawdust-packed S-shaped galleries under the bark and raised ridges on branches are common signs of infestation. It adds that adults typically emerge in early June through July, and that timing can help homeowners and arborists zero in on inspections.
What the city is doing
Edina's forestry crew has stepped up monitoring along streets and in parks and is advising residents on treatment options and removals. As reported by KSTP, Edina Forester Luther Overholt joined Minnesota Live to walk viewers through how to spot infected trees and when it is time to call for an inspection. The city's Parks & Recreation site outlines the forester's duties and notes that staff can inspect suspect trees, treat prominent public trees when feasible, and mark hazardous specimens for removal and replacement.
What homeowners should do
Experts are emphasizing basic stress reduction for oaks: deep, infrequent watering, adding organic mulch outside the dripline and protecting roots from soil compaction or construction damage. The Minnesota DNR cautions against pruning oaks from April through July to reduce the spread of oak wilt, and the University of Minnesota Extension says insecticide options, including systemic injections and carefully timed trunk or foliar sprays, can help in the early stages of decline. Those treatments are unlikely to save trees that have already lost roughly 40 to 50 percent of their canopy.
Where to get help
If you suspect an infested oak, you are urged to contact your city forestry office for an inspection; Edina residents can reach Parks & Recreation forestry staff for evaluations and guidance. Local extension and state forest-health resources list step-by-step diagnostic information and reporting guidance for oak decline, and certified arborists can advise on whether treatment or removal makes more sense for high-value trees.
