Updated 2:55 p.m. | Posted 11:49 a.m.
Minnesota agriculture officials said Thursday that emerald ash borers have been discovered for the first time in Chisago County, northeast of St. Paul, and that they expect to place the county under quarantine to restrict movement of wood.
Minnesota has roughly 1 billion ash trees, more than any state in the nation, and the trees are "highly susceptible" to destruction caused by the emerald ash borer, the Minnesota Department of Agriculture said in a statement.
Emerald ash borers have reached a critical mass and could rapidly become a much bigger problem in the state, said Mark Abrahamson, a department entomologist.
"Now it is kind of inevitable that it is going to spread and become a big problem," he said. "We're reaching a period where it may start to build and spread more quickly, and that's something that has been seen repeatedly in places where emerald ash borer has been found."
Officials said two adult emerald ash borers were found on a survey trap in Chisago along the Washington County border near Manning Trail, and that a follow-up visit "discovered tunneling consistent with invasive pest in a nearby tree."
Because it's the first time the pests have been found in Chisago, state officials say they're sending the specimens to a United States Department of Agriculture lab for confirmation, which is expected next week.
They added that Chisago will likely be put "under an emergency quarantine in the next week and eventually join Anoka, Dakota, Fillmore, Hennepin, Houston, Olmsted, Ramsey and Winona counties in a state and federal quarantine."
The biggest risk of ash borers spreading comes from people unknowingly moving firewood or other ash products harboring larvae, the department said.
The quarantine is meant to limit the movement of any items that may be infested with ash borers, including ash trees, ash tree limbs and all hardwood firewood.
Officials again urged people not to transport firewood and "burn it where you buy it." There's also a state website where people can read about the signs of infestation.
Emerald ash borer larvae kill ash trees by tunneling into the wood and feeding on the tree's nutrients. It was first discovered in Minnesota in 2009. The last county to be quarantined for the pest was Fillmore in April 2015, officials said.
Watch a Minnesota Agriculture Department video on the life cycle of the emerald ash borer:
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