Image: U.S. Department of Agriculture | CC BY 2.0

The Emerald Ash Borer, an invasive species of beetle that infests and kills ash trees, was discovered in Eau Claire County in December of 2017.  It’s been a slow crawl across the United States from Michigan, where the first cases of infestation were found.  Federal quarantines, which limit the transportation of firewood between counties, have been issued from the coast to eastern Nebraska and down into counties in northern Louisiana.

Dalton Larson, an ISA certified Arborist who owns Axe Tree Service in the Chippewa valley, helped cut the first tree confirmed to be infested by the ash borer in Milwaukee in 2009.  “Now that I go back there and see the damage, it’s devastating,” he said. “It’s a real destroyer of trees.”

The adult emerald ash borer is a green flying beetle that feeds on the leaves of the ash tree, and actually does little harm to the plant.  It’s the larva that causes damage.  Ash borers lay eggs under the bark of the ash tree, and when the larva hatch, they eat the vessels that transport nutrients throughout the tree.  This prevents the ash from getting those nutrients, causing crown thinning, weakening of branches, bark sloughing, prolific sprouting, and eventual death of the tree.  Oftentimes, symptoms of infestation don’t show until several years after the start, and by then, it takes a professional to determine the viability of treatment.

“Once the tree is infected, it’s pretty much a death sentence,” Larson said.

Landowners should be wary of this threat, Larson said.  This begins with identification.

Ash trees have opposing branches, which means that branches sprout on either side of a bough in a somewhat symmetrical fashion.  The same is true of the leaflets of an ash tree.  Bark of younger ash trees is smooth and gray-brown, while mature trees develop rigid bark in a diamond-like pattern.  A trained arborist can identify the trees on your land if you are uncertain.

Once ash trees have been identified, landowners must determine whether it’s worthwhile to protect the tree from infestation or cut the tree.  Preventative maintenance has a high success rate, saving the tree and helping fight the spread of the ash borer.  However, treatment should continue for as long as eight years.

Trunk injections and chemical and organic soil drenches are used to prevent and treat ash borer infestations.  These treatments kill all of the living things in the tree, including and ash borers.

“The earlier you can do it, the more success you will have,” Larson said.

If a tree is past saving or not worth protecting, it has to come down.  Tree removal services have a number of methods for cutting and felling trees.  While some removals can be tricky due to terrain, access to the tree, and other factors, professionals will determine the best methods for removing the plant.  Felled ash trees should be chipped into pieces no larger than ½ inch, burned, or covered to dry for at least two years.

Ensuring diversity of the tree population is a good way to minimize the effects of invasive insects, Larson said.  Landowners should aim to have no more than 30 percent of their trees be from the same family, no more than 20 percent in the same genus, and no more than 10 percent in the same species. 

“It’s gonna be a real problem in the next few years,” Larson said.  “Doing nothing is the main concern.”