New northern oak wilt detections

By Paul Cigan, forest health specialist, Hayward. Paul.Cigan@wisconsin.gov; 715-416-4920 and Linda Williams forest health specialist, Woodruff. Linda.Williams@wisconsin.gov; 920-360-0665

Oak wilt (OW) was confirmed for the first time in Bayfield and Douglas counties and in 16 new northern townships in 2018. The new OW infections occurred on a range of properties, including county, tribal, private, U.S. Forest Service and Board of Commissioners of Public Lands. Wisconsin Department of Natural Resources (DNR) forest health staff are working proactively with affected property managers and landowners to address these infections and prioritize disease prevention and detection in the future.

 

Oak wilt distribution map. Confirmed counties are displayed in red. Confirmed townships are displayed in pink 6-mile square blocks.

The greatest risk of overland transmission in northern Wisconsin is from April 15 to July 15, when fungal spores readily infect open wounds. Most of these new cases occurred during this time frame due to stem and branch damage. The primary causes of damage were roadside brush clearing, pruning, lot clearing and storm-caused branch breakage. Fungal spores may have come from diseased oak firewood and unprocessed wood recently transported into these areas.

Image shows a group of oak trees. Northern red oak on far left is in wilting stage of disease (leaves on but wilting and dropping). Oak on far right has mechanical root collar injury. Dairyland Township, Douglas County.

OW disease center. Oak on far left was infected through belowground root contact with tree damaged in lot clearing (far right). Dairyland Township, Douglas County (photo taken by Paul Cigan).

If oak wilt is present in or within 6 miles of the county where you manage oak, your management activities may be affected by seasonal harvesting restrictions to reduce OW introduction and impact. Read DNR’s oak harvesting guidelines for more information and refer to the list below of new 6 square mile blocks by township and county to see if OW has been detected near your property.

Bayfield County
Barnes T45N R9W
Cable T43N R7W
Drummond T45N R8W
Douglas County
Dairyland T43N R15W
Gordon T44N R11W
Langlade County
Elcho T34N R11E
Langlade T33N R13E
Neva T32N R11E
Sawyer County
Couderay T39N R8W
Hayward T41N R8W
Hunter T40N R7W
Round Lake T41N R8W
Spider Lake T42N R7W
Vilas County
Boulder Junction T42N R6E
Lac du Flambeau T41N R5E, T40N R5E
St. Germain T40N R8E

Please report any suspected oak wilt infections to your local DNR forester or regional forest health specialist and learn more about oak wilt identification and biology on the DNR oak wilt webpage. To learn more about firewood rules and how you can help reduce transmission of pests and diseases, including oak wilt, visit the DNR firewood page.

10 oak leaves lain on downed log display bronze discoloration typical of oak wilt. Midrib and base of leaf are still green.

Bronzed leaves fallen from infected oak. Leaves were observed beneath infected northern red oak. Cable Township, Bayfield County (photo taken by Paul Cigan).

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