An invasive insect that kills ash trees established itself in mid-Missouri as it spreads across the state, according to the Missouri Department of Conservation.

The state confirmed the presence of the emerald ash borer in 16 new counties this year, including Boone, Cooper, Howard and Randolph counties. The state has now confirmed the borer’s presence in 75 of Missouri’s 114 counties and St. Louis since the insect was first spotted in the state in 2008.

The borers live most of their lives inside ash trees, feeding on the tree and cutting off its supply of water and nutrients. Ash trees become brittle when the die and can be dangerous, said Robbie Doerhoff, Department of Conservation forest entomologist. That’s why the department is encouraging people to either treat or remove infested trees as soon as possible.

“They’re very, very dangerous to work around,” she said. “Just the slightest wind or even vibration from a bucket truck coming in to take the tree down can be enough to cause the tree to fall unexpectedly.”

The state typically confirms the presence of the emerald ash borer by investigating reports from private landowners and setting traps on public land. The insects found in mid-Missouri this year were mainly from traps on public property, she said:

In Cooper County, a borer was caught in a trap at an Interstate 70 rest stop near Boonville.

In Howard and Randolph counties, borers were caught in traps at the Rudolph Bennitt Conservation Area.

In Boone County, borers were caught in a trap at the Charles W. Green Conservation Area, on the University of Missouri campus, and at the MU Baskett Research Center.

The department sets the traps where they think they’ll find ash borers, Doerhoff said. A lot of people go to Rudolph Bennitt to camp, and they bring firewood that might be carrying the borers, so the department set several traps there, she said.

Borers are difficult for even experts like Doerhoff to detect, and the traps aren’t perfect. Unlike other insect traps, the emerald ash borer traps don’t use a pheromone to attract the insect. Instead, they attract them with their purple color, Doerhoff said.

“It’s kind of like winning the lottery to catch one because you have put the trap in the right place at the right time,” she said.

Borers are especially hard to detect in the first few years of an infestation, she said. Larvae inside the tree feed on the tissues that carry nutrients through it, cutting off the flow of water and nutrients as the infestation grows. After several years, they’ll eventually cut off the flow entirely and the tree will die, but it starts with leaves on larger branches higher up in the tree turning brown or not developing at all, she said.

The damage starts towards the top of the tree and takes a few years to work its way down. By the time the damage is at eye level, it’s too late to save the tree, she said. Another sign is if the tree attracts a lot of woodpeckers, which feed on the larvae. If a tree’s outer bark has been stripped, it’s likely popular with woodpeckers and could be infested, Doerhoff said.

If a tree has less than about 30 percent of its canopy damaged, it might still be possible to save it with insecticides, she said. People in mid-Missouri who have high-value ash trees on their property may want to start treating them next spring, she said.

“It would have been premature to treat them in mid-Missouri before the last few years,” she said. “You could have spent years wasting money and unnecessarily using pesticide by treating your tree.”

Doerhoff recommends only using insecticides that have been researched and proven effective. Two are available to typical consumers — imidacloprid and dinotefuran — and can be applied to the soil around the trunk, so long as the trees are less than 20 inches in diameter. Others are available to tree care professionals and can be injected into the tree or sprayed on it, according to a treatment guide from the Department of Conservation.

Those chemicals have to be applied periodically, making treatment a long-term commitment. Removing the trees, especially if they are already in poor condition, may be the easier and less costly move in the long run. People should check referrals and insurance before they hire someone to remove a tree, according to the guide. Removed trees should be burned, chipped or used as lumber near where it was planted to avoid further spreading the insect, Doerhoff said.

Native to Asia, the insects first arrived in Michigan in the early 1990s before spreading on lumber and firewood shipped from the area. They were first spotted in Missouri in Wayne County in 2008 and spread across the state, largely on infested firewood.

The borers typically spend their lives within a half-mile of the tree in which they developed, but they can travel longer distances, Doerhoff said. When they around found in a new location, she typically draws a 30-mile radius around the spot, assuming the insect could be anywhere in that area, she said.

“If they get up above the tree line and the wind catches them, they could go several miles,” she said. “But the massive movement across much of the eastern United States has primarily been the result of people moving them to new places, and then they can spread on their own from there.”

The borers have likely been living undetected in Boone County for 5 to 7 years. A lot of people who work in conservation and entomology live in the county, and they’ve been looking for it, she said. Even for people who know what to look for, catching an emerald ash borer is a matter of getting the right landowner report or setting up a trap in the right place, she said.

While the insects have likely been around the region for a few years, the drought affecting much of northern and central Missouri in 2018 could have helped the population grow quickly. Drought weakens trees, making them more susceptible to infestation, Doerhoff said.

People who suspect a tree has damage from emerald ash borers can report it by using the online form at eab.missouri.edu or by calling MDC’s Forest Pest Hotline at 866-716-9974.

bcrowley@gatehousemedia.com