Photo courtesy of Rainbow Treecare
Healthy Ash Tree
Ash tree canopy
The land of lakes is also the land of trees, including nearly 1 billion mature ash trees that provide a canopy over the state’s great outdoors. Sadly, in the past decade, an invasive pest has attacked and killed thousands of Minnesota’s ash trees—and threatens to wipe out many more.
First found in Michigan in 2002, this harmful forest insect from Asia known as the emerald ash borer (EAB) has spread quietly across the country, killing millions of trees in the U.S. and Canada. Minnesota’s first known infestation was discovered in 2009 in St. Paul. Today EAB can be found widely across the Twin Cities and beyond.
Here’s what you need to know to save your shade:
1. The emerald ash borer is not letting up.
Even though EAB has fallen from the headlines, it’s still here, slowly weakening and killing ash trees that shade everything from family cabins, backyards, parks, campgrounds, and city neighborhoods.
“It’s not nearly contained,” says Jeff Hafner, a certified arborist and director of municipal consulting with Rainbow Treecare in Minnetonka. “Minnesota adds new infested counties every year. If you have an ash tree anywhere in the seven-county metro area, it’s likely under attack, and the window for getting it protected is closing.”
Photo courtesy of Rainbow Treecare
Ash Tree Bark
Diamond pattern of ash bark
2. It’s an invisible danger.
The EAB spends its entire life cycle on ash trees, much of it under the bark, so evidence of infestation remains hidden.
“The adults feed on ash leaves,” Hafner says. “They lay their eggs on the outside of the ash bark, and when the larvae hatch, they burrow into the bark and feed under the bark for one or two seasons … then emerge as adults and repeat the cycle.”
3. The cold won’t save your trees.
EAB reproduces too fast, and winters in most of Minnesota are no longer cold enough to eradicate the pest.
4. Every ash tree in the Twin Cities is at risk.
Much of our community's public and private tree canopy consists of ash, and because EAB is widespread, everyone’s ash trees are at risk. Many people are passive in their appreciation of the trees in their yard or neighborhood until those trees are marked for removal, are blown down, or lose limbs. By then, it’s too late.
“When you start to see many trees being removed from neighborhoods and cities, [the effect] ripples out in both fiscal and environmental ways,” Hafner says. “That large shade tree is really difficult to replace.”
5. Without help, a death sentence.
Once infested, an ash tree usually dies in 3-5 years if not treated, Hafner says.
“Emerald Ash Borer is the most destructive forest pest this country has ever seen, because of how big the ash range is—essentially from Maine to the Rockies—north to south,” he says. “Hundreds of millions of unprotected trees will be killed, if not billions.”
Photo courtesy of Rainbow Treecare
Ash Tree Being Treated
Treatment for EAB
6. Treatment saves trees.
The good news is there are highly effective treatment options. If you have trees but can’t tell an ash from other varieties, consult an arborist. Hafner says an early sign of infestation is a thinning canopy on a once-thriving tree.
Treatment involves an injection at the base of the tree during the growing season. The tree naturally draws the treatment to areas where the ash borers feed—and kills them. The relatively inexpensive treatment is repeated every two years.
7. Treating trees is less expensive than removing them.
Treating a tree for EAB is less expensive than removing a dead tree, not to mention waiting 20 years for a new tree to mature. A dead tree can be hazardous and expensive to remove if it becomes brittle and unclimbable. Then heavy equipment must be used to take it down.
Plus, there are hidden costs to losing mature trees to EAB, Hafner says. “The impacts are really spread across a number of areas—your property value goes down and your cooling bills go up, especially if that tree is shading your house.”
8. Trees are infrastructure, and they increase in value over time.
For Hafner, working to slow the spread of EAB is about saving a valuable asset in communities across the state. Mature trees are a resource that many people take for granted.
“On a big scale, trees are infrastructure,” he says. “Trees are the only piece of infrastructure that increase in value over time, because they provide greater benefits as they grow larger.”
9. Trees help fight climate change.
By providing shade, trees lower demand for air conditioning, which in turn reduces electricity use—lowering carbon emissions at power plants. Mature trees also intercept rain, funneling it into groundwater and improving air quality by pulling pollutants from the air. (Of course, they do all of this while looking good.)
10. EAB is a public and private issue.
Hafner says he works with 30 municipalities that consider tree protection a key piece of their EAB strategy and offer discounted treatment prices to homeowners to do the same thing.
The more treated trees you have, the fewer insects you’re going to have. “Treated private trees benefit the public side and vice versa,” Hafner says, noting that EAB treatment should be considered part of annual household maintenance.
There’s no time to lose. EAB has a toehold in Minnesota and expands its range every year. Spring is a great time to consult an arborist and create a treatment or removal plan. The action you take this year could save your shade for years to come.
