It is an insect little bigger than a grain of rice. But the invasive emerald ash borer may as well be Godzilla for all the chaos it has brought to the Upper Midwest’s forested landscapes.
The borer has already laid ruin to the ash that dominated urban and lowland forests in Michigan, where it first turned up near Detroit in 2002, likely a hitchhiker on wooden shipping pallets from China. And in dozens of Wisconsin villages and cities, street terraces are marked by the stumps of ash trees already removed because of infestation.
The Wisconsin Department of Natural Resources says the borer has killed more than 50 million ash trees and is now found in a dozen states, including more than 30 counties in Wisconsin. Though it is not a threat to human health, the ash borer’s inevitable spread is likely to dramatically change the face of both urban and state and national public forests. The insect has already cost Wisconsin communities millions of dollars as they prepare for its assault and as they begin to remove and treat infested and threatened trees.
And it has proven a massive challenge to researchers—including entomologists at CALS—as they bring science to bear on understanding and slowing the march of the tiny, tree-killing insect and reducing its impact where it is established.
CALS entomologist Chris Williamson, who has studied the insect since 2003, says the word “cataclysmic” is not too strong to describe the eventual devastation that will be wrought by the emerald ash borer.
“The emerald ash borer means the demise of ash trees in North America,” says Williamson, who is also a UW–Extension specialist.
His colleague, CALS entomologist Ken Raffa, has researched and introduced parasitic wasps as potential predators that might help at least slow the insect’s steady march across the continent. But Raffa also said there is little doubt that such efforts are mostly holding actions against a foe that cannot be stopped.
“The genie is out of the bottle,” Raffa says.
Even so, in the face of what seems to be nothing but bad news, research at CALS and elsewhere has provided weapons that are proving effective at slowing the insect, giving communities time to plan and homeowners the ability to treat and possibly save treasured trees with insecticides.
In fact, Williamson, surveying a stand of ash trees he has treated and studied at Warner Park on Madison’s North Side, says he actually gets irked when someone says there’s nothing that can be done to save an ash tree. He has spent long hours in the field, testing various insecticides. And he has found that treating an ash tree early enough and repeating that treatment every couple of years can save even large, prized trees that homeowners want to protect. Insecticides such as emamectin benzoate, marketed under the brand name “TREE-age,” have also given urban foresters an effective tool to slow the loss of ash and temper the impact on a community’s cooling leaf canopy.
Treatment has also been found to be less expensive than was originally anticipated. Experts with Arborjet, a company that has worked with a number of communities on treatment, says that an injection treatment, in which the insecticide is shot into the tree through holes bored in the bark, costs on average $50 to $60 every two years for municipalities. The cost is more for individual homeowners, according to Arborjet, but still cheaper than removal and replacement.
Research by Williamson and others has shown that when it comes to protecting an ash from the voracious borer, action must be taken.
“If you have an ash tree you want to preserve and you don’t treat it, it will die,” says Williamson.
Continue reading this story in the Fall 2014 issue of Grow magazine.