When Dutch elm disease began killing trees in the Twin Cities in the mid-1970s, the replacements of choice were ash trees.
Ash trees were seen as a robust and hardy variety, and a disease resistant replacement for dying elms, whose canopies stretched along many miles of Minneapolis and suburban streets.
More than 40 years later that mature urban and suburban forest is under attack.
Emerald ash borer (EAB) has forced cities and private property owners to remove many of those trees, attempt to save some, and replace dying ones.
Eden Prairie has received more than $156,000 in grants from Hennepin County since 2019 and another $42,000 from the Department of Natural Resources to conduct tree inventories, remove and replace diseased ash trees, educate residents about the value of trees and increasing the number of trees for capturing carbon, reducing air pollution, taking up stormwater, and providing shade to counteract the urban heat island effect.
In September, the county awarded 21 Healthy Tree Canopy grants totaling about $404,000. Grants will fund projects in nine cities, 10 affordable housing properties, four schools, and through five nonprofit organizations, including congregations and neighborhood associations. More than 1,000 trees will be planted through the grant projects.
Eden Prairie received $43,949 to plant trees in various parks, treat high priority ash trees, and remove 100 trees in 2022.
Work is currently being done in parks on the western side of the city, including Wyndham Knolls, Hidden Ponds, Riley Lake Park, Round Lake Park and others.
Eden Prairie Schools also received $8,940 to replant 82 trees where ash trees have been removed.
EAB in Eden Prairie
EAB entered Eden Prairie about four years ago and was first confirmed in the northeast part of the city, according to Lauren Stufft, the city’s forestry and natural resources specialist.
The city initially focused its efforts on the eastern side of the city and has moved west as the ash borer spread. The insect can fly about a mile a year.
Stufft said that the city’s efforts focus on maintained park areas. Last year’s winter surveys identified almost 800 trees that had been infected and she expects even more this winter.
“In the next two years, even untrained eyes will begin wondering why there are so many dying trees,” she said.
The city is treating about 400 trees a year, Stufft said. Her primary concern now is the large number of ash trees on private property that some people don’t even realize they have.
“I’ve run into quite a few people who don’t think they have an ash tree and they actually have 10,” she said.
To solve that problem, Stufft urged residents to contact a professional tree service that employs certified arborists. Most companies with provide a free consultation, she said.
Signs of infestation
Adult EAB are small, iridescent green beetles that live outside of trees during the summer months. The larvae are grub or worm-like and live underneath the bark of ash trees. Trees are killed by the tunneling of the larvae under the tree’s bark.
Early in an EAB infestation, a tree will appear to be healthy, Stufft said. Eventually, woodpeckers begin doing damage to the upper level of the tree in search of the larvae hidden beneath the bark.
After leaves have fallen, inspectors can easily spot the distinct “S” shaped larval galleries using binoculars.
Eventually, the canopy dies back from the outside in, Stufft said.
While trees that are showing signs of disease need to be removed, Stufft said that treatment could be the most cost-effective decision for healthy trees, especially large ones in difficult-to-remove locations.
Removal of those trees could cost $6,000 to $7,000 she said, dwarfing the cost of ongoing treatments. Removing smaller trees ranges from $500 on up.
Stufft said it is too late to treat trees this year, but she recommended calling a tree service to get on their list for first thing next spring. The city has partnered with a local tree service to provide discounted treatments.
Homeowners need to determine if they have ash trees and decide whether to treat or remove them soon. If city inspectors spot a diseased tree on private property, they could be marked for removal. The homeowner is responsible to remove marked trees on their property.
Homeowners also need to take care when disposing of diseased ash trees.
All of Hennepin County is under EAB quarantine by the Minnesota Department of Agriculture (MDA), which means the public cannot transport any hardwood from Hennepin County to a non-quarantined county.
Most of the spread of EAB has been through the transport of infested wood, such as firewood.
Eden Prairie will plant 250 trees thanks to the Hennepin County grant, Stufft said.
Unlike when elm trees began dying, there will not be a single species selected to replace ash trees.
“What we’re trying to do now is plant a large variety of replacement trees,” Stufft said. The city is planting about 50 different types of trees in hopes of avoiding a large die-off in case of another invasive insect species.
Among trees being planted are disease-resistant elms, but also lesser known varieties such as Northern Catalpa, Kentucky Coffeetree, and Ohio Buckeye. A complete list of recommended trees for Eden Prairie is available on the city’s website.
Replacement trees are about 1.25 inches in diameter, Stufft said. Some come from local Minnesota nurseries, but others come from a large nursery in New York, where thousands of trees are purchased in combination with surrounding cities and Hennepin County and shipped to Minnesota.
As winter approaches and trees drop their leaves, Stufft said she will continue applying for grants.
“It really helps cities stay on top of EAB to avoid having trees dead and standing,” she said.