Don't Prune Oak Trees From April Through July: Oak Wilt

Mar 23, 2017

Credit Max Pixel FreeGreatPictures

There was snow on the ground Thursday in the Northwoods but a DNR spokesperson says be careful about doing pruning on oak trees  April through July.

Every county in Wisconsin with the exception of Forest, Iron and 9 other counties have the tree disease Oak Wilt. Paul Cigan is a DNR plant pest and disease specialist....

"...it's a disease that clogs up the water-conducting tissues of oaks and it tends to be more severe in the red oak group, including the Northern Red Oak, Northern Pin Oak, and Black Oak, which are all native red oaks to Wisconsin. It tends to be less severe in White Oaks although White Oaks can still get the disease, but they tend not to be as affected by it...."

Beetles are attracted to the oak wound, and bring with them oak wilt spores which then affects the trees vascular system. Cigan says not transporting infected firewood can go a long way to preventing the spread of the disease. He says to protect trees in general, don't move firewood long distances, or only use firewood labeled as Wisconsin certified. He says if an oak loses a branch between between April and July, use some type of tree paint to prevent the beetles from visiting a tree.

While counties in the north like Oneida and Vilas have been found with oak wilt, he says much of northern Wisconsin is still free of the disease, unlike the southern two-thirds of the state. There's a longer interview with Paul Cigan below.

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