DULUTH — The discovery of the emerald ash borer in northwestern Wisconsin has led to a quarantine on transporting wood that could become an issue for Minnesota mills.

The quarantine prevents the moving of firewood out of Wisconsin’s Douglas County, but it also kept the region’s timber industry from transporting unprocessed ash trees through the end of the month.

Jon Harris, the director of Douglas County’s forestry department, said loggers and mills alike will be affected.

“Every level of that supply chain is going to feel a certain level of pain,” he said.

Duluth officials said it’s only a matter of time before the invasive insect crosses into Minnesota. Already the bugs have created problems on the other side of the St. Louis River.