The battle continues: Naperville’s war on ash borer infestation

Naperville has been using treatments of different insecticides to fight the emerald ash borner. | File photo
Naperville has been using treatments of different insecticides to fight the emerald ash borner. | File photo

The city of Naperville’s ongoing war against the emerald ash borer infestation isn’t over by any means, but officials say that progress is being made as far as saving trees.

Members of the city’s Public Works Department team, led by forestry supervisor Jack Mitz, are working daily throughout the city identifying trees at risk as well as treating others that are not infested. Their efforts, as City Manager Doug Krieger puts it, are keeping Naperville “ahead of the curve.”

“Unlike some other cities, we jumped ahead of the curve and began treatment before a lot of other cities did, and this has really helped maintain our urban forest,” Krieger said. “Some people waited one or two years before doing anything and by then, it’s too late. A lot of places have had to treat this with chainsaws.”

The ash borer problem dates back to 2008. At the time, there were 17,300 parkway ash trees in Naperville. According to Christine Schwartzhoff, operations team leader for the Public Works Department, the number today stands at around 15,000 or a 14 percent loss over the past six years due to the borer.

“Last year, the city removed 700 ash trees,” Schwartzhoff said. “In the past two years, removals have essentially leveled off to around 700 to 800 per year.”

Treating trees before they are infested has proven to be effect. Mitz said that while trees in the eastern portion of Naperville have held up better than those in the western portion, the number of losses at this time “is manageable.”

“We have been using a product that has been very effective on large trees, but less so with smaller ones,” he said. “Certain neighborhoods seem to be effected more than others. We monitor trees and check all of them and those that are rated ‘poor’ or ‘dead’ are removed.”

Mitz confirmed that around 700 to 800 trees will be lost again this year. He describes the number as “manageable and not overwhelming.”

“It’s not like we have dead trees all over the place,” he said. “We’re still in the mindset of treating those trees that are healthy.”

Schwartzhoff said that the current mortality rate for ash trees here in Naperville “is counter to the exponential mortality curve” experienced elsewhere, thanks to the effective treatment of healthy trees.

“The science has shown that untreated tree populations will start off losing trees slowly and then deaths will grow exponentially, eliminating the entire population in a few short years,” she said. “Basically at this point, Naperville should be seeing dead trees in the thousands, not hundreds.”

Naperville is spending $475,000 on emerald ash borer treatments in 2014. All healthy parkway ash trees are getting treatment with insecticides Xytect (imidacloprid), Safari (dinotefuran) or Tree-Age (emamectin benzoate), Schwartzhoff said. Overall, the Tee-Age treatment has proven to be the most effective.

“In the two years since we started treating comprehensively, only 1 percent of those treated with Tree-Age were removed,” she said.

The biggest lingering problem seems to be those trees located on private property where treatment is the homeowner’s responsibility.

“We do have places in the city where, as I noted, things have not held up as well, and there are a lot of dead trees,” Mitz said. “The thing is, this ends eventually as there is only so much food and there is this huge production of (borers) and then the population crashes. The (borers) are still around, but then things kind of back off.”

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