Did The Polar Vortex Kill Off Emerald Ash Borer?
Over the last 15 years or so, most discussion regarding insect survivability dealt with how warmer temperatures have increased the range of southern and exotic insects into Wisconsin. The polar vortex of 2013-14 has flipped that discussion around and now the question is - just how many of these insects were able to survive the coldest winter in Wisconsin in 30 years?
In the Midwest this winter, the question has centered on the exotic emerald ash borer (EAB) insect. This Asiatic invader has killed millions of trees in Wisconsin and is a severe threat to our ash trees.
Hopeful reports from Minnesota suggest that extreme cold could kill a large percentage of EAB larvae overwintering in our trees. A study by Vanette and Abrahamson in 2010 projected that when the temperatures drop to -10o F, 34% of EAB larvae die and if temperatures fall to to -20o F, 79% of larvae will die in the cold. This study was performed using cut logs placed in freezers, which is a far cry from the normal, natural surroundings.
Before we get our hopes up, more knowledge of the EAB and tree biology may be in order. In January, EAB expert Deb McCullough of Michigan State University reported that many insects adapt to cold weather by producing chemicals that prevent their cells from freezing and rupturing in cold temperatures. Insects such as the EAB begin producing these “anti-freeze” chemicals in the fall and the process accelerates as winter progresses. The trees that provide safe harbor to the EAB during winter also undergo a similar acclimation process. Trees draw water out of their cells to prevent freezing and cell rupturing. Larger trees have thicker bark protection that can also shield larvae. In addition, micro climate factors can cause variability in air temperatures and can have a great impact upon the mortality percentage of EAB larvae.
In short, insects and the trees they shelter in become adapted to cold weather over a period of time. Sudden cold snaps, especially those that occur in late fall or early winter before the acclimation process has begun, are most likely to cause EAB larvae mortality. There is a chance that the polar vortex of 2013-14 killed off some larvae, but it would be unwise to alter EAB management plans expecting large scale death of EAB larvae.
Emerald ash management plans consist of taking stock of how many ash trees you have and deciding how much you value them. Preventative treatments such as soil insecticide or trunk injections can protect ash trees. Properties with large ash tree populations may want to consider management strategies that are multi-faceted and include treatments, removal and replanting efforts.
Hoppe Tree Service offers plant health care programs that are custom designed to fit your needs and requirements.