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Can City's Canopy Stand Up Against First Sign of Emerald Ash Borer?


The City of Milwaukee has joined a club of which no community wants to be a member.

Late last week, officials announced that the Emerald ash borer has infected trees on the city’s northwest side.

WUWM Environmental Reporter Susan Bence met a city forester on the site to learn how Milwaukee has been preparing for the pest.

It has already taken down tens of millions of trees in states to our east as well as in Canada.

David Sivyer inspects a once majestic 60-year-old tree on West Mill Road.

“Let’s see if there’s a one’s that has the characteristic shape,” Sivyer says.

The forestry manager spots a miniscule yet distinctive “d-shaped” hole.

That’s where a mature ash borer emerged from the tree.

During its larval stage - it made its home beneath the bark and ate away at critical tissue.

“And as they grow they feed on the wood and that creates these serpentine galleries and so the affect of that is that it disrupts the plumbing system if you will, so the tree can no longer pick up water from the soil and move it to the leaves where it’s needed,” Sivyer says.

Sivyer estimates the beetles have been slowly starving this and neighboring ashes for several years.

“They feed and they grow and develop in the tree and emerge as adults and mate and then lay eggs in other ash trees and the cycle continues.,” Sivyer says.

A colleague spotted the ravaged trees late last week. Sivyer says, just a year ago, these trees looked healthy.

“That’s pretty typically with this pest – it’s very elusive – very difficult to detect; and it’s not until the tree expresses symptoms that you can really discover it.,” Sivyer says.

Not all that long ago, emerald ash borer wasn’t even part of Sivyer’s urban forestry vocabulary.

That changed in 2002, when its first infestation hit the other side of Lake Michigan – in Detroit. Sivyer stopped planting ash trees in 2006.

Two years later, his department carried out an “urban tree canopy assessment”.

“We knew we had 33,000 ash street trees that were ours to manage,” Sivyer says.

Crews started injecting chemicals into most of the city’s ashes – the healthiest and most established ones.

Sivyer says the treatment regime works like a charm.

“But we didn’t have any idea how many trees in our city were at risk. And that study found that we had 587,000 ash trees at risk in our city,” Sivyer says.

A grant allowed Sivyer to supplement that basic data with aerial photography. Aircraft charted every ash in the cityscape.

Then the city dispatched college interns - armed with maps and brochures - to knock on doors.

“And They identified 9600 households that had ash trees on their property. We reached about 34 percent of the property owners, caught them at home; informed them that they had an ash and emerald ash borer was a problem and was coming and they needed to prepare for it; and the others, we left information at the door. So we have done we think what we can to help not only the city to prepare, but to help our residents to prepare,” Sivyer says.

Now that the emerald ash borer has surfaced in this northwest side neighborhood, Sivyer hopes a visual tool – just down the street - delivers the “time is running out” message.

City ash trees protected by chemical injections

“There’s a block of ash street trees that have been protected by chemical treatment, that we’ve injected, that are looking perfectly fine. In spite of the drought, they look green; they’re healthy and so this demonstrates that the treatment does work and that there are options other than removal to citizens, but they need to act now,” Sivyer says.

All Sivyer can do when it comes to trees in people’s yards is offer seasoned advise.

As for the city’s trees, for now, treating them chemically makes financial sense.

“Our cost to inject with city personnel is about $70 per tree and the cost to remove and replace that same tree is about $750,” Sivyer says.

Sivyer says by warding off a massive ash borer infestation, the city hold on to its canopy that provides not only shade, but improves air quality by capturing carbon, not to mention slows down storm water run-off.

The forester says his choices are dwindling when it comes time to replace ash.

“Unfortunately the pallet of species that we have that will tolerate urban condition; you know the compacted soils, the heat loading just the inhospitable conditions to grow trees; those that will tolerate that is a pretty small list. So by losing ash, and just like we lost American elm, we’re losing the ability to diversify and protect the city against future invasives, future diseases,” Sivyer says.

Sivyer’s forestry team is trying a new strategy – planting a variety of species, instead of lining entire blocks with a single type of tree.

“Our goal is to have no less than four species in each block,” Sivyer says.

So when the next pest arrives on the scene, it won’t wipe out an entire block.