Emerald Ash Borer may threaten county trees

Landowners advised on how to avoid, fight damaging insects

“There’s a good chance it may be here and we just haven’t found it yet.”

That was the message from Iowa Department of Natural Resources District 3 Forester Joe Herring provided to area landowners Tuesday on how to avoid a “green menace” insect that can kill off ash trees: the Emerald Ash Borer (EAB).

He said a 2015 survey of Marshall County trees “didn’t turn anything up” for evidence that the EAB inhabits the area, but added several surrounding counties have at least one infested ash tree.

Herring described the insect’s life cycle to a full classroom of concerned county residents and landowners at Grimes Farm and Conservation Center.

“The larvae is the stage that causes the damage,” he said. Audience members saw a preserved larvae-stage EAB up close in a small, glass vessel. Herring also passed around a chunk of ash wood that had been bored into by the insects, creating a small, distinct D-shaped hole.

“The Liberty Bell-shaped segments are unique on the EAB larvae,” he said of the larvae’s body shape.

The small, iridescent green adult form of the insect is nearly harmless, Herring added. The damage to ash trees comes when the newly-hatched larvae bore into the tree and eat and grow. When the larvae pupate out, they bore their way back through the tree bark, where they lay more eggs.

Once an ash tree is infested, the insects typically work from the top of the tree down to the base, a process which Herring said can kill a tree in 6-8 years.

“They tend to re-colonize the same tree,” he said.

Herring also gave the background on the insects’ arrival in the United States and, eventually, central Iowa. The first reported issues with ash trees began in 2001 in Detroit, Mich.

“They figured out it was this species of beetle, the EAB,” Herring said. “They figured out it had arrived in Detroit … on shipping crates.”

Since then, the insect’s range has grown out of Michigan and has reached as far west as Colorado, according to information in Herring’s presentation.

To protect central Iowans’ ash trees, Herring suggested landowners be careful about bringing ash firewood to their property. Although EABs are relatively poor flyers, they spread quickly with the help of humans.

“Many communities have a lot of ash trees,” Herring said, adding some communities have ash trees accounting for as much as 40 percent of their canopy.

Once a tree is infested, or when an infestation is within about 15 miles of an apparently unaffected ash tree, Herring said an insecticide may be the best option.

In his presentation, Herring showed three insecticide treatment types based on the size of the tree at “breast height,” or 4.5 feet above the ground.

For trees larger than 20 inches in diameter at breast height, Herring said to go with a professional service for treatment. He said this often involves directly injecting insecticide into the tree body, minimizing outside contamination.

For trees between 12 and 20 inches in diameter at breast height, Herring said a homeowner can use the “soil drench” method of application around the base of the tree.

For trees under 12 inches, the suggestion was for the homeowner or landowner to use a granular spread around the tree.

“Every (insecticide) product that you buy has a label,” Herring said, encouraging the audience to read and understand the potential risks for surrounding flora and fauna by using powerful insecticides. “So far it’s been proven very effective.”

There are several institutions with detailed information on the EAB and what homeowners can to do protect their ash trees, Herring said.

Websites he suggested included Iowa State University Extension and Outreach at https://store.extension.iastate.edu/Product/Emerald-Ash-Borer-Management-Options and the DNR website.