In Ontario, Canada, the city of Hamilton has an aggressive plan to combat the Emerald Ash Borer, and it’s not too different from that of St. Paul’s.
In short, cut down everything. A choice selection from their website:
EAB has the potential to destroy Hamilton’s entire ash tree population of approximately 23,000 trees in the next 10 years. City council approved a proactive plan to remove 10% of Hamilton’s ash tree population each year for the next 10 years. Each ash tree that is removed will be replaced with a new species of tree to help diversify Hamilton’s urban forest.
Some call that approach burning the village to save it. In Minneapolis, however, the news is pretty much the same. On the city’s website, Minneapolis officials call infestation and ash tree decline inevitable:
All ash trees … will become infested with EAB and eventually die. … Waiting to remove ash trees until they become infested is not an option because the trees will die in such large numbers that it will not be possible to keep up with removal and replacement. Proactively removing trees before they die reduces the risk of damage and injury caused by limbs falling from dead and dying ash trees.
With state support, city officials in St. Paul are focusing on removing infested or declining ash trees, but they’re pretty much resigned to losing every single ash tree over the long haul.
It’s a scorched-earth approach that not everyone deems necessary. J. Michael Orange spent 31 years as a city planner in Minneapolis. Two years after he retired, the dreaded Emerald Ash Borer larvae was discovered in the city, launching aggressive efforts to remove infested or unhealthy ash trees in Minneapolis. The first infected tree was discovered in St. Paul in 2009.
Orange, now a private environmental consultant who lives in St. Paul, has spent the past year researching alternatives, and he’s convinced they exist.
His new study argues that it’s actually more expensive to remove ash trees from a city’s tree canopy than it is to treat healthy, “high quality” trees with pesticides and leave them standing indefinitely. He notes that pesticide costs have fallen as research and availability has improved.
One such product is Emamectin Benzoate (EB), sold on the market by ArborJet as “Tree-Age.” “High-quality trees can be preserved with EB for well beyond 20 years for the cost of removing and replacing them,” Orange said.
That’s one pesticide, but there are others. More on EB here: http://www.emeraldashborer.info/treeage.cfm#sthash.6FS7cJSP.dpbs and here: http://www.ncbi.nlm.nih.gov/pubmed/21539242.
Orange points to examples such as Burnsville and Oakdale, cities that are trying to be pro-active about spraying trees in advance of the Emerald Ash Borer’s arrival. Milwaukee, which has a documented infestation, is also spraying in hopes of keeping larvae numbers from reaching an explosive tipping point.
The good folks in Kansas City, Missouri’s Parks and Recreation Dept. don’t seem too convinced about the benefits of preemptive spraying, at least beyond 15 miles of a known infestation. This is from the “frequently asked questions” on their Emerald Ash Borer website.
What about insecticides? Should I begin to use them to protect my ash trees from EAB? Preventative insecticide applications are generally not recommended if known infestations are not within 15 miles of your location and/or found within your county. Premature use of insecticides is ineffective, wastes money and needlessly adds chemicals to the environment.
More on the environmental concerns here.
Nevertheless, some critics believe that instead of leaving streets virtually empty and denuded, cities should spray select, “high quality” trees in the public domain with pesticides. The hope is to keep the ash borer away from healthy trees that can yet be saved.
Back in January 2011, a handful of like-minded folks eager to preserve rather than remove ash trees formed the Coalition for Urban Ash Tree Conservation. Their ranks included the parks superintendent in Elgin, Illinois and a handful of horticology and entomology professors in Illinois, Michigan, Ohio and Wisconsin, as well as an agricultural scientist in Connecticut and some private tree care groups.
They acknowledged in their Jan. 6, 2011 mission statement that “some structured removal / replacement of unhealthy ash” was important and inevitable, but they said each city and state’s overall emphasis should be on retention, not removal. Their philosophy has achieved mixed reviews.
Orange notes that it wasn’t until 2008 that the U.S. Environmental Protection Agency began approving pesticides for use against the invasive species.
That’s raised worry that long-term side-effects of those pesticides aren’t fully known, and that companies that tout pesticides as cure-alls are more interested in making a buck or selling snake-oil than helping a community out.
St. Paul officials have also expressed concerns about the financial risk — treatments would have to be applied indefinitely, every two or three years, at hefty long-term costs. While the supplier slowly gets rich off tax dollars, a whole lot of chemicals would be entering the environment.
Orange believes that St. Paul’s cost estimates are out of whack. While he’s no expert on pesticides or on the specific situation in St. Paul or Minneapolis, his study weighs preservation costs against the cost of preemptive trees removals.
“I can only speak generically. The study is called the ‘Generic Ash Tree Preservation Plan,’” Orange said. “It’s half the price, the treatment over a 20-year period of time, to preserve four times the tree canopy.”
Where do those cost savings come from? While St. Paul’s ash tree canopy is about 30 percent of the city’s tree cover, his model is based on a hypothetical city where “high quality” ash trees constitute about 14 percent of the tree population. To get down to that number, he focuses on preserving healthy trees in public boulevards, and excludes trees in woodland areas.
He writes, over email:
Our model focuses on high-quality ash trees, which I explained are healthy trees properly located (e.g. located in boulevards and in public areas that the public frequents such as the front yards of public buildings and the mowed areas of parks). It does not include trees in woodland areas where the public rarely go except along trails or roads. For our model, which is based on a typical city in the region, high-quality trees constitute only 14% of the total ash population.
Municipal leaders are pretty dubious. Since being discovered in southeastern Michigan in 2002, the pest has killed upwards 22 million trees across the United States and Canada, and many state and city officials seem resigned to remove and replace their municipal ash tree canopy, which is no easy task.
Ash trees constitute about a third of the tree cover in St. Paul, and the city removes about 1,000 of them per year, replanting them with much smaller trees from a variety of species. Conservative estimates have it that about one in five of the metro area’s tree cover is ash tree, according to Orange’s study.
Over the years, researchers have had more questions than answers about the effectiveness of insecticides. Here’s a June 2009 study produced by the North Central Region Integrated Pest Management Center.
St. Paul does, in fact, spray some 300 trees per year. Orange believes, however, that even more aggressive efforts to preserve rather than tear down the ash trees would save the city money in the long run.
THE DEATH CURVE
Orange said it takes at least three to four years for an infestation to build before a tree shows sign of decline, “and then it explodes.” That’s called the ‘death curve,’ and it hasn’t really hit St. Paul yet in force. We’ll know when it happens.
By some estimates, a single Emerald Ash Borer female can produce a trillion offspring in nine years, or 50 trillion in 10 years.
“Cities were utterly overwhelmed,” he said. “That’s the experience out east. Now, ours is a satellite infestation. Somehow infested wood got here. Also, in Minneapolis. Also, in Winona and Superior. It’s slow.”
He believes that proper treatment can shape or slow the death curve, stalling tree deaths and keeping the ash borer population from ever reaching the tipping point where their numbers grow exponentially.
Could we get a reprieve this year because of the long, bitterly cold winter?
“Maybe this winter is going to slow it down yet,” he said. “We don’t know yet. It could be this summer when thousands of trees start dying.”
St. Paul has been trying to create a bit of a buffer around known infested areas by removing unhealthy trees in the vicinity, but skeptics worry that preemptive removals will make the insect fly even further to find new food sources, inadvertently hastening the spread. The bugs can fly up to six miles.
Brian Aukema, an Assistant Professor of Forest Entomology at the University of Minnesota, isn’t quite convinced either way. He writes, via email:
I’d … disagree that tree removal spreads the EAB problem because EAB have to fly farther to find food. Michigan and Ohio have suggested this, and it’s certainly reasonable, but it’s almost impossible to prove with data.
Some scientists believe that trees within a 15-mile radius of a known infestation are already infested, prompting spraying efforts in places like Burnsville and Oakdale.
“Because it’s difficult to detect … if your city is within 15 miles of a known infestation, it is wise to begin treatment,” Orange said. “And that’s what these cities are doing.”
Either way, costs will stretch into the millions. Dying trees drop limbs on power lines and pose a threat to people, a huge financial liability for municipalities.
Nevertheless, Orange is convinced that cities “can cut the costs in half” through treatment. He acknowledges, though, that no city has found a silver bullet to get rid of Emerald Ash Borer for good.
After recently focusing on the East Side and Highland Park, city work crews on Friday began removing ash trees along both sides of Lexington Parkway.
They’ve posted information online at the Emerald Ash Borer website at www.stpaul.gov/eab. The city forestry department can be reached at 651-632-5129.