Oak wilt is a deadly fungal disease that can decimate oak dominated forest. The oak tree, once infected, succumbs to mortality within a matter of weeks to a few months. The fungus effects oaks within the red oak family (Northern red oak, Northern pin oak, black oak, etc.) with white oak being much more resistant to the disease. Unlike other forest health issues (like emerald ash borer) there is certainly hope to minimize damage done, by this non-native disease, due to the way it spreads.
The disease moves to new host trees in two ways: above and below ground. To enter an uninfected area the fungus must first be introduced above ground. This requires the help from a sap beetle to facilitate its movement from a fungal spore pad (forms on a decease tree the following years after death) to the wound of a healthy tree. The sap beetle is attracted to the fungal spore pad’s smell and feeds on the pad. While feeding the fungal spores attach to the beetle and catch a free ride to the next wound(s) the beetle visits.
Once the infected tree dies the disease can also then spread through the below ground method. Due to the nature of how oaks grow, adjacent tree’s roots grow together and create root grafts. This gives the fungus an underground network to leave the tree it has killed and move on to nearby healthy oaks. The disease will continue to spread if root grafts are present to the next adjacent tree(s).
So how do you prevent and mitigate oak wilt?
The best management is prevention. Oak wilt can certainly traverse the landscape without human intervention due to natural events, like storms and high winds, that create wounds on oak trees. However, sap beetle movement is often limited due to the abundance of wounds to feed on in the area after these natural events. Long distance movement often occurs due to human-made wounds. Sap beetles have been documented to sense a wound, and travel, up to 5-10 miles to feed. These sap beetles are active during all times of the warm season (spring, summer, fall) but are most abundant during April 15 – July 15.
To best avoid oak wilt entering your oaks it is highly recommended that oaks are not cut, pruned, or damaged in any way during April 15 – July 15 (Michigan Department of Natural Resource recommendations). To use the highest of caution, stretch this time frame out to October 15.
If you unfortunately do have oak wilt enter your oak tree(s) immediate action can help avoid the spread. Contact an Oak Wilt Certified Arborist or Forester to help you plan and implement mitigation. Above all, perform constant monitoring of your property, and the oak trees present, to identify any oak wilt disease infections.
For more information on this disease visit the following links: