University of Minnesota Extension

Extension > Local Extension Offices > Stearns > County Horticulture Educator > Articles > Freezing Out the Emerald Ash Borer

Freezing Out the Emerald Ash Borer

University of Minnesota Extension, Stearns County News
March 12, 2014        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns & Benton Counties


Freezing Out the Emerald Ash Borer
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (03/12/14) — After going through a deep freeze this winter, many may wonder, what will happen to the Emerald Ash Borer (EAB) population?  Did the Emerald Ash Borer freeze out?  Unfortunately the short answer is no, but the deep cold may have caused mortality to some of the population. 

A recent report by Rob Venette and Mark Abrahamson predicted that “when larvae reach 0°F, 5% will die; at -10°F, 34% will die; at -20°F, 79% will die; and at -30°F, 98% will die.”  Air temperatures definitely reached low temperatures throughout Minnesota this winter.  The coldest temperatures recorded in Central Minnesota this winter, according to Weather Underground, were flirting around -20 to -25°F on several occasions.  Death rate of the Emerald Ash Borer larvae will likely not be exactly known, but it is promising news that the freezing temperatures killed off a decent percentage of the larvae in the state. 

The Emerald Ash Borer has not yet been discovered in the central part of the state; however it has been discovered in Minnesota.  The Emerald Ash Borer was found in Ramsey and Hennepin counties in May of 2009, and found in additional counties thereafter.  Since 2002 the Emerald Ash Borer has already killed tens of millions of ash trees in North America.  Minnesota has a lot at stake with having the largest concentration of ash trees in the entire country, with nearly a billion ash trees in our forestland and urban areas.

This winter’s cold temperatures have likely caused higher mortality levels of the Emerald Ash Borer, which in turn has slowed its population growth; however it did not eliminate the pest from our state and will not justify a change to the management strategies.   Emerald Ash Borer populations will likely rebound and reach tree-killing levels once again in our state.
Knowing what you can do is critical. The most important thing to remember is to not transport firewood unless it is MDA (Minnesota Department of Agriculture) Certified. It is illegal to move all hardwood firewood out of the EAB quarantine counties of Hennepin, Ramsey, Houston and Winona unless it is MDA Certified. Preventing the rapid spread of the Emerald Ash Borer can only be done by not transporting firewood from other parts of the state or even out state sources. On its own, the EAB will generally move only about 1/2 to 1 mile a year from infested sites. 
Another key component is to watch for signs of infestation in your ash trees. Symptoms of an Emerald Ash Borer infestation are unusual sprouts on the trunk, 1/8 inch, D-shaped exit holes in the tree’s bark, where the borers have exited the tree once they’ve matured to adults, also woodpecker pecks, and vertical bark splits on the ash trees.  This may not be definitive EAB infestation, but it may indicate you should take a closer look.  After peeling back some bark where there is a crack, look for distinct “S” shaped galleries, where the larvae have been eating through the different layers of the wood.

Treatment is available, and University of Minnesota research is showing signs of success; however do not apply insecticide treatment unless you are located within 15 miles of a known infestation. Removal of healthy ash trees on your property is not necessary. The best prevention is awareness, and not transporting firewood unless it is MDA Certified.
Finally, report any suspected infestation, know the exact location, take digital pictures if possible, and contact the MDA “Arrest the Pest” hotline at 888-545-6684 or via email at


Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
  • © Regents of the University of Minnesota. All rights reserved.
  • The University of Minnesota is an equal opportunity educator and employer. Privacy