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Ash trees in distress: Identifying the culprit

Published: Monday, Jan. 13, 2014 11:00 a.m. CDT • Updated: Wednesday, Jan. 15, 2014 11:05 a.m. CDT
The emerald ash borer is shiny green with a cigar or torpedo shaped body. It is about 1/2 inch long and 1/8 inch wide.

Editor’s note: This is the first in a three-part series on the emerald ash borer and how to tell if a tree has been attacked, prevention and treatment to stop or slow the spread of the destructive beetle .

Do you have an ash tree in your yard?

Could it be infested by the emerald ash borer (EAB)?

Those questions and more were answered during a public meeting Thursday evening at SuperTel Inn and Conference Center.

Mark Shour, Iowa State University Extension and Outreach entomologist, explained the particulars of the EAB and how it affects trees.

Many in the room packed with nearly 100 people had concerns because of the December discovery of an infected tree in a residential area near the center of Creston. Shour said once infestation is found, the emerald ash borer has probably been in the area for about three years.

The emerald ash borer is a small beetle that kills all species of ash trees, including green, white, black and blue. The federally regulated insect was found in four Iowa counties along the eastern side of the state before the discovery in Union County.

“Emerald ash borer has a one-year life cycle,” Shour said. “It starts out as an adult. They come out anytime between June and August. They don’t live that long, but it’s staggered and they’ll come out beginning of June through August.”

He said the adults only live three to six weeks and lay 40 to 70 eggs, which hatch into larvae.

“The larvae is a very flat insect that feeds on the bark,” he said. “They’ll feed from June until frost. They’ll live over winter under the bark. That’s a great time to find them, right now. If you’ve got a tree that is suspect you’ll find the larvae under the bark.”

The larvae makes a serpentine, or S-shaped, pattern under the bark. The last two or three segments of the larvae body are shaped like a school bell.

The insect

Shour said after maturity the adults then have to get out from under the bark and leave a distinctive D-shape hole in the bark where they exit.

“This is one of symptoms you see for emerald ash borer,” he said. “It can’t be a round hole. It can’t be an oval hole. It’s got to be a D-shaped hole.”

An adult EAB is about 1/2 inch long and 1/8 inch wide.

“If you find something that is shiny green and it’s longer than that or doesn’t look like a cigar or torpedo, it’s not an emerald ash borer,” Shour said. “You want to narrow down your choices to this specific insect.”


He said EAB also does not create saw dust, and if sawdust is detected, it is not emerald ash borer.

Adult female EAB do feed on the edge of ash leaves for about a week, but does not cause much defoliation.

Shour said most of the infestation starts at the top of the tree and then works down from there. Early infestation is usually found when the tree is being trimmed by someone using a bucket lift.

“The crown of the tree starts thinning, then right below where the larvae are working you’ll get a whole bunch of these water sprouts, ... sprouts that pop out,” he said. “What the tree is trying to do is trying to out grow the damage.”

But, he said, the EAB tends to stay in one tree until it is depleted before moving to other trees.

“I went to Detroit, Michigan, for a learning experience several years ago and an ash tree that I saw was probably 50, 60 feet tall, and I saw from the root flare all the way to the top of the tree nothing but tunnel after tunnel after tunnels after tunnel,” he said. “It wasn’t like get in and then leave. It was like they keep using the resource until the resource is completely used up.”

Shour said woodpeckers may be another symptom of an EAB problem.

“Woodpeckers do quite a bit of work and you can see what is called flecking, it’s lighter bark and you can almost see it from the ground,” he said. “You definitely could see it with a pair of binoculars.”


Shour said the most susceptible tree to EAB are those that are stressed, but that is not always the case.

“The age is not as important because I’ve seen emerald ash borer in one-inch diameter trees all the way up to huge trees,” said Shour. “And they will attack healthy trees as well as stressed trees.”

For more information on the EAB visit the Iowa State Extension website at https://www.extension.iastate.edu/pme/emeraldashborer.html.


Tuesday: Identifying the ash tree and prevent option of emerald ash borer.

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