When Dutch elm disease hit Minneapolis in the 1970s, the city aggressively removed the damaged trees and was able to save some of the giant elms lining the boulevards.
That will not be the case with ash trees infested by the emerald ash borer.
“All ash trees are at risk, and all of the infected trees will die,” Peggy Booth of the Minneapolis Tree Advisory Commission told members of the City Council’s Regulatory Services, Energy and Environment Committee.
“We really have five new areas of the city that now have confirmed emerald ash borer as of late winter,” said Booth.
Ash trees are a major part of the urban forest in Minneapolis, with 38,000 on public land and an estimated 175,000 on private property.
The Minneapolis Park and Recreation Board is aggressively removing ash trees from city golf courses, where they account for nearly a quarter of the tree population.
The advisory commission is recommending that 5,000 additional public ash trees be removed this year in conjunction with road projects and along power lines.
The removal project would target smaller trees and up to 20 percent of the ash per block throughout the city.
“We are losing all of our big trees and their benefits,” said Booth. Most of the ash on public land are 12 to 14 inches in diameter and stand about 40 feet tall. In contrast, the diseased Elms were frequently twice that size and cost much more to remove.
With Dutch elm disease, there was the possibility of treating healthy trees to avoid infestation. That is also an option for ash.
The city of St. Paul and the Minnesota State Fair are both treating 2,000 to 3,000 ash trees. The Minneapolis Tree Commission has not ruled out the use of insecticide on high-value trees but is not looking at that as a major option.
“It is not without controversy,” said Booth. “There are concerns about the use of chemicals related to pollinators, related to water, and there is mixed research in relation to that.”
The emerald ash borer was first discovered in Minneapolis in 2010, and the size of the problem has grown each year.
“Because we know the trees are going to die from emerald ash borer, we can get a little bit ahead of the curve on the removal part,” said Ralph Sievert, director of forestry for the Minneapolis Park and Recreation Board, which manages all of the city’s boulevard trees and those in city parks.
“You can’t really wait until you see the trees dying because when the tree does die, it falls apart quickly,” said Sievert, adding that an ash can go from healthy to deadfall in eight months’ time.
Minneapolis Tree Advisory Commission
The removal of ash trees has been slowed by storm cleanup, which also has also cut into the watering of young boulevard trees, placing them at risk.
“The city can’t get to them [young trees] while they’re doing the emergency storm response,” said Booth, who urged residents to help out by watering the young boulevard trees. “Now is the time. It’s hot this week, we haven’t had appreciable rain and they don’t have an established root system yet.”
Residents with young boulevard trees can request a Gator bag from the Park and Recreation Board that makes watering trees easier and comes with instructions.
Storm clean up will set back the ash removal schedule by an estimated six weeks, Booth said.