MANITOWOC COUNTY, Wis. (CBS 58) — Oak wilt, a deadly disease that affects oak trees, has been detected in Manitowoc County for the first time, according to the Wisconsin Department of Natural Resources.

The DNR announced Friday that DNA testing confirmed the presence of Bretziella fagacearum, the fungus that causes oak wilt, in a tree in the town of Mishicot.

The tree was planted in the mid-1980s and is believed to be a hybrid of bur oak and swamp white oak.

The property owner contacted the DNR after noticing symptoms consistent with oak wilt. As of Nov. 6, the tree is the only confirmed case in Manitowoc County.

The nearest known oak wilt infections are about 20 miles away in Brown County.

"It's possible that oak wilt has been present in the area at low levels for many years," DNR forest health specialist Bill McNee said. "Alternatively, someone could have recently introduced the disease into the local area through infected oak firewood or logs."

The DNR said the overall impact of oak wilt in Manitowoc County is expected to be limited because oak species make up less than 2% of the county's forest trees and about 1% of its urban trees.

Other tree species are not affected by oak wilt.

The disease is common across the southern two-thirds of Wisconsin, including Milwaukee County, and has increasingly been detected in northern parts of the state.

Oak wilt has now been confirmed in 67 of Wisconsin's 72 counties. Nearby Calumet, Door and Kewaunee counties have never had a confirmed detection.

One of the most noticeable signs of oak wilt appears during mid- to late summer, when affected branches begin to wilt and leaves fall earlier than expected.

"These are not the brown, dry leaves you see in autumn," McNee said. "These are often partially green and partially bronze."

The fungus can be transported to new areas through infected firewood, logs and other raw oak materials. Beetles that feed on sap from tree wounds can also carry the fungus from infected trees to healthy ones.

The DNR recommends avoiding pruning or injuring oak trees between April and July, when the risk of spreading oak wilt is highest.

If an oak is cut, pruned or damaged during that period, the DNR recommends immediately sealing the wound with water-based paint or pruning sealant.

The agency also encourages people to keep firewood local and leave oak firewood or uncut logs where they were harvested for at least one year, or until the bark becomes naturally loose.

Once an oak becomes infected, the disease can spread to nearby trees through connected root systems and over longer distances when beetles carrying the fungus are attracted to fresh wounds.

The DNR said preventing oak wilt from reaching a new area is significantly easier than trying to contain it after an infection has been established.