The spread of the destructive emerald ash borer marches on, with Fillmore County, to the south of Rochester, the latest county to be hit by the pest, the state Department of Agriculture reported late last week.

Once federal agriculture officials confirm the infestation, as soon as this week, Fillmore will join other counties in its part of the state (Houston, Olmsted and Winona) and four in the Twin Cities area (Anoka, Dakota, Hennepin and Ramsey) subjected to a quarantine.

The evidence in Fillmore was found in Rushford in the form of suspected emerald ash borer (EAB) larva and feeding activity in a boulevard ash tree. The discovery was made during a routine visual survey by the state Department of Agriculture.

The quarantine puts limits on the movement of any items that may be infested with EAB, including ash trees and ash tree limbs, as well as all hardwood firewood.

EAB larvae kill ash trees by tunneling into the wood and feeding on the nutrients. Since its unintended introduction into North America, EAB has killed tens of millions of ash trees in 24 states.

The invasive insect was first discovered in Minnesota in 2009. Minnesota is highly susceptible to EAB's destructive tendencies. The state has roughly 1 billion ash trees, the most of any state.

State officials say there are three easy ways to stem the spread of EAB:

• Don't transport firewood. Buy firewood locally from approved vendors, and burn it where you buy it.

• If you live in a quarantined county, be aware of the restrictions on movement of products such as ash trees, wood chips and firewood.

• Watch ash trees for infestation. If you think your ash tree is infested, go to www.mda.state.mn.us/eab and use the "Does my tree have emerald ash borer?" guide.