An invasive beetle is spreading rapidly across the state.
This week, the Missouri Department of Conservation reported the emerald ash borer appeared in 11 more counties in 2018, bringing the total number of affected counties in the state to 53. The larvae of the metallic green beetle burrow under the bark of ash trees and kill them within a few years.
The emerald ash borer was found for the first time this year in Adair, Callaway, Cape Girardeau, Cole, Greene, Jefferson, Lewis, Lincoln, Pike, Polk and Warren counties. The insect has been present in St. Louis and St. Louis County since 2015 and St. Charles County since 2014.
“We have foresters that cover every county,” said Missouri Department of Conservation forest entomologist Robbie Doerhoff. “We train them to be on the lookout for emerald ash borer.”
The beetle, originally native to Asia, was first detected in Missouri in 2008.
Since then, humans have inadvertently aided the spread of the insect by moving firewood from place to place.
“Once the emerald ash borer is put into a new area by humans, usually accidentally, then it’s able to very quickly move on its own,” Doerhoff said. “The females will usually lay eggs on the same tree they came out of, but occasionally, females will go up to 12 miles away.”
Adults emerge from ash trees in mid-April, leaving behind distinct D-shaped holes in the bark. They later mate and lay eggs on the trunk and branches. During this period, they spend most of their time high up in the tree canopy and can be difficult to find.
The larvae do most of the damage to ash trees, creating grooves in the wood that interfere with the flow of water and nutrients within the tree.
According to the Missouri Department of Conservation, the emerald ash borer kills more than 99 percent of ash trees within three to four years of initial infestation.
Of the 80,000 trees along public streets in the city of St. Louis, more than 15,000 are ash trees. The St. Louis Forestry Division expects a large proportion of these trees will have to be removed as the emerald ash borer spreads across the city.
Although ash trees are the primary host for the emerald ash borer, the beetle can also develop on several other species, including Missouri-native white fringe trees.
Certain pesticides are effective against the emerald ash borer, but Doerhoff recommends prioritizing healthy, high-value trees.
“In order for these insecticides to be distributed throughout the tree properly, your tree needs to have a healthy vascular system,” she said. “These are trees with nearly full canopies, that don’t have a lot of wounding or bad prune jobs.”
Pesticides specific to the emerald ash borer are available at hardware stores and are often most effective on small trees with trunks less than 20 inches in diameter. The Missouri Department of Conservation recommends waiting until spring to apply them, when pesticides are most likely to kill the beetle.
A professional forester can treat larger ash trees by injecting pesticides directly into the vascular system of the tree.
Based on the rapid spread of the beetle across Missouri in the past 10 years, Doerhoff said it will likely colonize the rest of the state within the next five years and eventually infest most ash trees.
“People really need to identify the trees in their yard and figure out if they have an ash,” she said. “If they want to keep it, they are going to have to treat it.”
To report a possible emerald ash borer infestation in a county that has not yet been confirmed, call the Missouri Department of Conservation tipline at 1-866-716-9974.
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