The Pioneer Press on Sunday published a front-page article on how different cities are responding to the Emerald Ash Borer, a dreaded beetle that infests ash trees with its larvae, gradually destroying large sections of city canopy.
The article examined varying approaches to the pest in Chicago, Milwaukee, Oakdale, Burnsville, Minneapolis and St. Paul, as well as Hamilton, Ontario.
Here’s a few more thoughts on the subject.
ST. PAUL PARKS AND REC COMMISSION
A recent study from Michigan State University estimates that the ash borer probably arrived in North America in the early 1990s, at least 10 years before it was discovered in southeast Michigan, an indication that many cities may already be infested with the pest but don’t know it yet.
Andrew Trcka, chair of the St. Paul Parks and Recreation Commission, said he doesn’t foresee the commission urging the city to change course on its Emerald Ash Borer strategy, which calls for removing about 1,100 dead or declining ash trees each year from public boulevards and right-of-way. That would rid St. Paul of all its city-owned ash trees within 20 years, or sooner if it can free up the funds.
He was impressed that city crews were keeping the commission apprised of the bug even before it was first discovered in South St. Anthony Park in 2009, and the commission continues to get updates.
To slow decline, St. Paul is injecting about 1,600 of the 28,000 remaining city-owned ash trees with insecticides, but city forestry officials say they have no reason to believe they’ll defeat the beetle. “We haven’t had a ton of cause, at least from my perspective, to kind of question how they’re treating it,” Trcka said.
THE PROFESSOR
To the horror of neighboring residents, the city of St. Paul recently removed ash trees up and down Lexington Parkway. It’s a decision that rests fine with forest insect specialist Brian Aukema, a professor with the University of Minnesota’s Department of Entomology.
“Excellent idea to remove those trees,” Aukema said. “We want to reduce the number of ash borers on the landscape. Those trees are infested. They’re going to die. Even at low densities, they’re close enough to the existing infestations that we know eventually will erupt. … I hate to see the trees go as much as the next person.”
Nevertheless, he finds insecticide products such as Arborjet’s “TreeAge” line increasingly promising, though he has some concerns about cities and homeowners situated more than 10 or 15 miles from a known infestation spending too much money too soon on injections, which have to be reapplied every two or three years.
This year’s frigid winter, he figures, reduced the ash borer population for a year or two at most, but it will bounce back. Aukema, who lives in northern Dakota County, hasn’t injected his own ash tree, but he figures it’s about time for cities in his area to start.
“We only have 10 years of data, but injections of Emamectin Benzoate can keep a tree alive (despite) some pretty thick infestations,” Aukema said.
“I think the results are quite promising. It becomes a question of scale. Is it economical or practical to inject every single tree in a city if you have thousands of ash trees? Do the inventory, decide what you want to replace, what you can sacrifice, and what the insect will take for you.”
THE TREE CARE CONSULTANT
Burnsville maintains 18,000 public ash trees, in addition to more than 22,000 on private property. The city’s EAB plan sets aside funds to treat 2,865 ash trees in parks and boulevards beginning this year. Out of 1,100 poor condition public ash trees, half will be replaced with new trees.
Those plans came together with the help of Jeff Hafner, a consultant with Rainbow Treecare, who has also worked with Columbia Heights to map out strategies against the Emerald Ash Borer.
Neither city has a documented infestation, but officials believe they’re close enough to infected sites in Minneapolis, St. Paul, Fort Snelling and Shoreview that they’d better be prepared.
Hafner believes that insecticide injections every two or three years can save the healthiest, most high-value trees, such as those along public boulevards. Trees already in a heavy state of decline are expendable.
“It has to be tied to what is the city’s goal,” Hafner said. “Because municipalities are so strapped with budgets that consistently decline … (many cities) don’t have the budgets to get (ash tree removals) done in 10 years. Mathematically, they cannot. You’re buying yourself some time, and you’re preserving the benefits” of the canopy, he said.
THE CITY FORESTER — OAKDALE
In Oakdale, city officials plan to inject trees with insecticides prior to the Emerald Ash Borer’s arrival — assuming it’s not there already.
City forester Chris Larson figures that Oakdale is home to roughly 700 ash trees in public boulevards and city-maintained areas. Current plans call for injections of the insecticide TreeAge on a three-year rotation.
“We’re treating right now 102 of our ash trees. and we’re looking to bump that up … which would bring us up to 267, now that some of the chemical treatments are becoming more affordable, and there’s science behind the claim that they last longer,” Larson said.
Larson said studies have pointed out the long-term social costs when cities lose trees and create a grittier landscape. There are also indirect but ultimately costly environmental impacts to the taxpayer because trees prevent nutrient loading in waterways and soil erosion.
“We’ve used (software) to calculate how much our trees are paying us with environmental benefits,” he said. “That’s where it gets somewhat hard to sell. … It’s not an immediate return on your budget.”
Oakdale’s trees are examined based upon a rating system, and those with cavities, open wounds or other evidence they’d be prone to fail in a storm or otherwise die off soon are targeted for removal. “We’re kind of doing a mixed-approach. We’re treating a bunch of trees, but we’re removing the lower condition trees,” Larson said.