Linden Borer in Minnesota

A few weeks ago, I ran across a pest that I have not seen in years. Our client had concerns about his Basswood trees dying back and issues with flaking bark. It turned out these trees were completely infested with some type of boring insect. So, I made a call to the Minnesota Department of Agriculture and had one of their entomologists, Angie Amborn, stop out to inspect the trees with me.

We found extensive damage throughout the property due to Linder Borer. In total, seven Basswood trees had to be cut down. There are two remaining Basswood trees on the property that are less impacted. We are currently working on a plan to treat these trees with a pollinator friendly product.

Here are some quick facts regarding Linden Borer

  • Tree species that are affected by Linden Borer include: Linden, Basswood, and Poplar.
  • Damage symptoms can be characterized as canopy die back, broken trunks/limbs
  • Detection of an infestation can be found during routine inspections June-Sept
  • Things to look for are: Frass flows from exit holes, round exit holes from roots/branches 6 mm in diameter
  • Mortality risk is high
  • Treatments are difficult, the only way to treat larvae is through a trunk injection. (Being that Basswood trees are pollinated, we have to be careful of which products we use.)