Now the real battle begins.
This could be the summer, say tree experts, when the infestation of the emerald ash borer reaches a tipping point for an assault that will kill almost every ash tree in the state.
“Everyone is holding their breath right now,” said John Masonick, owner of Monster Tree Service in Lake Elmo.
Officials recently announced the bug’s arrival in Cottage Grove. It hit Burnsville in May, and is expected to spread soon to every metro-area city.
Tree services are informing homeowners they must make one of three unpleasant choices:
- Remove healthy ash trees to prevent the spread, and replace them with another species.
- Treat healthy trees with insecticide. This does rescue trees, but it also means they require the shots every two years to survive.
- Do nothing, and wait for the trees to be infected. At that point, there is no cure — and neighbors will be angry because your sick tree will be infecting their trees.
The time to procrastinate is fading, said Leo Afanasyev, co-owner of Eagan-based MSP Tree Service.
“We are absolutely seeing more of this,” he said in late May. “Just today we removed two big, beautiful trees in Roseville.”
The problem is more advanced than it appears, because the symptoms take two years to show up.
“If you have an ash tree in the Twin Cities, you should be treating it right now,” said Monster Tree’s Masonick.
The beetle, which is native to Asia, was first discovered near Detroit in 2002. So far, it has infected 50 million of the 700 million ash trees in Michigan.
Minnesota could be an even bigger banquet for the bug — with a billion ash trees.
STARTED IN 2009
The green insect made its Minnesota debut in 2009 in St. Anthony Park in St. Paul. It has been spotted throughout the Twin Cities, in Duluth, in Martin County near Fairmont, and along the Mississippi River southeast of the metro area.
The insect cannot be stopped, but tree experts have laid out strategies to slow it down.
St. Paul is spending $1 million a year to remove ash trees and replace then with other species.
Cottage Grove is removing 275 trees this year, most of them ash. It will inject another 700 ash trees.
The city has about 3,000 ash trees, out of 16,000 boulevard trees and trees on manicured parkland. That does not include thousands of trees in wild areas, where the bug is expected to spread unchecked.
Cottage Grove forester Quinn Palar is replacing the ash trees with a variety of other species. That way, he said, an unknown predator won’t be able to wipe them all out in the future.
“This is our strategy for the next big pathogen,” he said.
TREATMENT CAN HELP, TEMPORARILY
Healthy trees can be injected with insecticide. Tree services pump the fluid into the tree trunks, where it circulates throughout the tree. But they must be treated every two years — and if that schedule is missed, the beetle could quickly return.
For treating ash trees with insecticide, Timberline Tree Service of White Bear Lake charges $14 per inch of diameter, or $140 for a 10-inch-wide tree.
“When we treat a tree with insecticide, it’s just a Band-Aid,” said Timberline arborist Kelby Nelson. He said the insecticide treatments can be continued indefinitely, but as soon as they are stopped for any reason, the bugs can move in. “Whatever you do, eventually the trees will die — it’s inevitable,” he said.
Despite the ongoing tree-thinning by cities, Nelson does not recommend it for homeowners.
That’s because the spread of the insect is unpredictable. “We were told that in one season it could cover the whole state. But it has been here for years, and is moving extremely slowly,” he said.
Nelson said that removing an ash tree may minimize the risk of spreading the disease to neighbors’ trees, but won’t eliminate it. “You will still have it in the area,” he said.
MSP Tree Service charges about $1,300 to remove a tree with a 10-inch diameter trunk, and $250 to remove the stump.
IS YOUR ASH TREE INFECTED?
Tree experts say an ash besieged by the emerald borer will have:
- Dead limbs or branches throughout the tree, starting at the top.
- D-shaped holes in the bark, about one-eighth of an inch long.
- Woodpeckers on the upper branches, digging in to eat the beetles.
- “Blonding” of the upper branches. This is caused by woodpeckers stripping bark, leaving branches smooth and pale-colored.
For more information, visit the University of Minnesota Extension page at www.extension.umn.edu/garden/insects/find/emerald-ash-borer/.