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While many of us Midwesterners had a break from shoveling snow and bundling up this year, the lack of persistent winter temperatures poses a serious problem for ash trees. As the Midwest has remained unseasonably warm, we skipped over those long periods of temperatures below freezing. This means that we missed the natural opportunity to control emerald ash borer (EAB), an increasingly destructive invasive beetle.
Pictured: A close-up of an emerald ash borer Credit: David Cappaert
The cold winter temperatures in the Midwest have major effects on emerald ash borer by slowing down their life cycle. Emerald ash borers typically live as larvae burrowed within the tree layers for 1-2 years. When winter temperatures remain warm, emerald ash borer larvae can continue feeding for longer periods which allows them to speed up their life cycle. This means the larvae will become adults faster, enabling them to reproduce sooner. This creates new generations of emerald ash borer at a rapid rate, increasing the chance of spread. Additionally, emerald ash borer larvae can not survive prolonged temperatures below -30 degrees F. Historically, these temperatures have been common enough that they have significantly slowed the spread of emerald ash borer in the St. Croix watershed. With climate change warming our winters though, there will likely be more opportunities for emerald ash borer to spread to previously unaffected areas in MN & WI.
Another factor to think about when considering the impacts of emerald ash borer is the lack of water we are entering the spring with. In a usual year, snowpack melts as spring temperatures warm which supplies water for the landscape. Just like us, trees need water and lots of it. When a tree is not getting enough water, they become stressed which makes them more susceptible to emerald ash borer.
Pictured: Characteristic identification features of a Green ash tree Credit: USDA ARS
With the lack of cold temperatures and potential drought conditions, our ash trees are in more danger than usual. If you would like to help slow the spread of EAB, see if you can ID an ash tree next time you're outside. Look for their branches that grow directly opposite from one another, compound leaves, and 5+ leaflets. Take a moment to look at the health of the tree and any tell-tale signs of emerald ash borer. This includes missing bark towards the top of the tree (known as “blonding”), dead branches, D-shaped bark holes, or sprouts at the base of the trunk. If you suspect emerald ash borer, please notify Report a Pest in MN or contact your local UW-Extension office in WI. Also, keep your firewood local to avoid spreading the larvae to uninfested areas. If you would like to learn more about emerald ash borer, infestation projections, and actions you can take, please check out our Emerald Ash Borer Lunch n’ Learn with Research Biologist, Rob Vennette.