Oak Wilt Disease in Wisconsin Forests

Arborists in Wisconsin say action must be taken to protect oak trees in the southeastern portion of the state from spreading oak wilt disease. While oak wilt disease has been present in Wisconsin for a long time, the cousin of Dutch elm disease has been becoming more prevalent in the state of late.
“It’s getting worse and worse,” tree care consultant David Farina said of the ongoing spread of oak wilt disease, which is spread via the trees’ roots or by beetles. “It’s certainly not under control,” agreed Dennis Fermenich, city forester for Greenfield, Wis. “I’ve seen it progress at a rather steady pace.”
Oak wilt disease typically takes at least a few weeks to kill an infected tree, making the tree shed its leaves and eventually succumb. Tree owners can protect their trees by not pruning them between April and September and by using injections of fungicide to kill the fungal infection.

• WHAT IS OAK WILT? Oak wilt is a tree disease caused by a fungus called Ceratocystis fagacearum. In the last twenty years Austin neighborhoods have lost an estimated 10,000 oak trees worth millions of dollars to this incurable disease. Oak wilt CONTINUES TO KILL valuable oak trees in Austin at alarming rates despite easy preventive measures that can prevent it’s occurrence and subsequent spread.
• HOW DOES IT SPREAD? The oak wilt pathogen is transmitted in two ways: (1) BY INSECTS: Sap-feedng beetles can carry oak wilt spores from a diseased red oak tree to fresh wound(s) on an uninfected oak, thus, introducing the disease for potential spread.
• (2) THROUGH INTERCONNECTED ROOTS OF TREES: Once a insect introduces the oak wilt fungus into an oak tree (perhaps through a fresh wound from trimming or wind breakage), the fungus can then spread rapidly from tree-to-tree via a network of interconnected roots. Mechanical trenching machines are then used to sever the roots systems to separate the diseased tree(s) from nearby healthy trees. Currently, this is the only effective way of stopping the underground (localized) spread of the disease.

• WHAT ARE THE BEST WAYS TO PREVENT THE SPREAD OF OAK WILT? (1) IMMEDIATELY TREAT “ALL” FRESH WOUNDS ON “ALL” OAK TREES DURING “ALL” TIMES OF THE YEAR WITH AN APPROVED TREE WOUND DRESSING/SEALER: the very best times to trim oaks to avoid contracting oak wilt is during the hottest months of the summer (July through September) and again in the coldest months of the winter (November through January). During these periods, the spring or fall months, please consult a professional / certified Arborist who is familiar with the oak wilt fungus, and all precautionary trimming techniques such as; tool sterilization prior to trimming, and painting of the wound immediately after cutting.
• (2) REMOVE DISEASED “RED OAK” IMMEDIATELY: Spanish oak and black jack oak are two examples of RED OAKS in the Austin area that can be responsible for harboring infectious oak wilt spores. After these trees contract oak wilt and die, the oak wilt fungus can form “fungal mats” under the bark of these dead trees. These are the sources where insects contract the disease spores on their bodies, and spread them to other healthy trees allowing the disease cycle to continue. It is therefore extremely important that these infected trees be immediately removed and promptly destroyed or buried in a city / county landfill. DO NOT KEEP THIS INFECTED WOOD FOR FIREWOOD, as insects will seek out and feed upon any fungal mats in the infected wood and potentially spread the disease spores to other nearby oaks.