Menomonie’s tree cover is undergoing a dramatic change. So far about 120 ash trees have been removed from city parks and boulevards in 2022. This is due to the emerald ash borer (EAB), a tiny green insect that is responsible for damaging and ultimately killing ash trees. The EAB first appeared in Dunn County in 2020.
According to the Department of Agriculture, “Emerald ash borer larvae kill ash trees by tunneling under the bark and feeding on the part of the tree that moves nutrients up and down the trunk.” Infected ash trees will lose most of their canopy within two years and die within three to four years.
The EAB is native to Eastern Asia. It arrived in the US accidentally with cargo from Asia in 2002 and is considered an invasive species.
Despite all of the cutting this year, Richard Henning, the city forester considers Menomonie lucky.
“Our previous mayor, Dennis Kropp, was aware of the emerald ash borer problem and stopped planting ash trees,” said Henning. “That put us ahead of the game.”
Comparatively, the City of Eau Claire has removed 6,800 ash trees since 2017.
Many municipalities planted ash trees to replace elm trees lost to Dutch Elm disease years ago. Infected ash trees can be treated, but it is expensive, and the treatment needs to continue for the life of the tree.
The worst of the ash trees have all been removed from city property, and the stumps will be removed in the fall.
Henning notes that trees are evaluated for removal based on criteria of public safety, disease, condition, and location, in that order.
“My job is to maintain and prolong the life of trees in the city, not remove them,” said Henning. “We only remove poor quality trees and are planting trees to replace those we take down.”
The city is trying to keep any one tree from making up a large percentage of the tree population, so that future diseases affecting one specific tree won’t be so damaging.
The most common tree found in Menomonie is currently the maple. Henning is diversifying the urban forest by planting a wide variety of trees including buckeye, hackberry, ginkgo, honey locust, ironwood, white oak, linden, and several others.
Henning only monitors city trees, those found in parks, boulevards, and other public places. Homeowners should be monitoring ash trees on their properties. Ash trees can be identified by their leaves, branch pattern, seed clusters, and bark. See the below diagram.
Signs of an infestation include thinning or yellowing of leaves in the canopy, small D-shaped holes on the trunk, which are signs of the emerging adults, or large portions of the bark falling off the tree. If not treated, the tree should be cut down. Ash trees will get very brittle, very quickly and become a danger.