Ash Tree Alert

The tree-boring pest killing ash trees in southeastern Michigan was recently identified as the emerald ash borer, an Asian pest previously unknown in the United States, according to Michigan State University researchers.

Though it’s no surprise that ash trees are suffering – Michigan ash trees have had a number of problems in recent years with diseases such as ash yellow and ash decline, which are brought on by drought, poor growing conditions and secondary pests that kill stressed trees, pointed out Deb McCullough, forestry entomologist, Michigan State University, East Lansing, Mich. – this year the problem escalated. “There was a high number of ash trees dying in southeastern Michigan and no one had identified what was causing the high mortality rate until this year,” McCullough said.

Because of the misdiagnosis on some of the ash tree deaths, the emerald ash borer gained a good strong footing in Michigan, pointed out Arnold Farran, research and technical director, J.J. Mauget, Arcadia, Calif. “Usually you can isolate a problem like this pretty quickly, but because of the misdiagnosis not only has the insect been identified in five Michigan counties (Macomb, Oakland, Livingston, Washtenaw and Wayne), but also is rumored to be moving to the surrounding states as well as crossing the border to Windsor, Canada,” he explained.

Emerald ash borer larvae are between 10 and 14 millimeters in length, and 10-segmented and cream-colored with a small brown head and little pincer-like appendages on the rear end, McCullough described. They feed on the tree’s phloem and outer sapwood, producing S-shaped galleries that look like roadways. Adult beetles chewing their way out of the tree leave distinctive D-shaped exit holes on branches and trunk.

Most infested ash trees die in two to three years. It is estimated that the pest has been in Michigan for at least five years.

“There are more than a dozen other insects that bore into dying ash trees, but this one is different because it infests quite healthy trees as well as stressed trees,” McCullough said. “So far, it has only been found in ash trees, but it can apparently kill all species of ash, including green, white and black ash, as well as several horticultural varieties.”

Currently, the Michigan Department of Agriculture (MDA) has imposed a quarantine to stop ash trees, logs and firewood as well as ash tree nursery stock from leaving the affected counties. Current injection treatments being used include the active ingredient Imidacloprid.

McCullough and Farran advised lawn care operators in Michigan and the surrounding states to keep an eye out for this insect. “It gets active in the spring and then again at the end of summer until mid-fall,” Farran said. “You don’t want this critter overwintering if you can help it. Since it had three years to gain a foothold, it’s making the Asian Longhorned Beetle look like a small issue.”

The author is managing editor of Lawn & Landscape magazine and can be reached at nwisniewski@lawnandlandscape.com.