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Emerald ash borer

Five years after the invasive emerald ash borer was detected in Douglas County, the spread of the destructive insect appears to be approaching its peak — it’s led to the removal of close to 150 ash trees so far this year and around 800 since it first arrived.

The insect, a type of beetle originally from Asia, was first detected in Douglas County in September 2015. City of Lawrence Horticulture and Forestry Manager Crystal Miles said that the infestation follows a bell curve, and that the peak typically occurs after about five years. Miles said that treatment and other favorable conditions, such as rainfall amounts, have helped the city’s ash trees stay healthier, but that overall the community appears to be approaching that peak.

“We think we’ve slowed the bell curve slightly, but we’re not going to stop it,” Miles said. “It’s still going to reach a peak, and at that point more trees are significantly impacted.”

The larvae of the insect kill ash trees by feeding under the bark, forming tunnels that block the tree from distributing nutrients. An update on the city’s emerald ash borer mitigation program recently provided to the City Commission states that the city is now experiencing the effects of the exponential growth of the pest. So far this year, the city has had to remove 144 ash trees, compared to a total of 101 trees that had to be removed in 2019. The city has treated 306 ash trees so far this year, compared to 289 in 2019.

In this Oct. 26, 2011, file photo, forester Jeff Wiegert of the New York State Department of Environmental Conservation, points out the markings left from emerald ash borer larvae on an ash tree in Saugerties, N.Y., at the Esopus Bend Nature Preserve.

The city’s program includes ash tree treatment, removal and replacement. As part of the treatment program, the city’s forestry division injects trees that can be saved with an insecticide that kills the larvae, and trees must continue to receive injections to survive. For ash trees on city property that cannot be treated, the forestry division removes them and plants another species of tree in their place. So far this year, about 100 new trees have been planted to replace ash trees, according to the update.

There are approximately 10,000 ash trees in Lawrence, with about 3,200 of those trees on city property and therefore under the city’s care, Miles said. She said that of the 3,200 city-managed ash trees, about 25%, or about 800, have had to be removed thus far. Miles explained that the city must remove the trees because as the insect’s larvae burrow under the tree bark, limbs weaken and can fall, potentially hurting people or damaging property.

“Once the ash (trees) start to die and decline, they become very brittle and they are not safe anymore,” Miles said. “They are more prone to structural failure.”

When the city first funded the emerald ash borer mitigation program in 2016, it was estimated that at least $3 million would be needed to address the issue over the next seven years. The city has removed 809 ash trees since the beginning of the program, is currently treating 732, and has planted 550 replacement trees in addition to the city’s existing tree planting program, according to information Miles provided the Journal-World. The city did not immediately have an update regarding how much has been spent on the program thus far, as Miles said that budget information is combined with horticulture, forestry, park maintenance and other city project funds related to street trees.

As the insect will eventually infect 100% of the ash trees in the city, Miles said private property owners should also be watching their ash trees for signs of infestation. Signs begin with the thinning of leaves, and Miles said bark can be peeled off of infested trees to reveal the tunnels. She said the city recommends removing trees when they are more than 30% dead, which property owners can do themselves or through a licensed tree trimming service.