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Oak Wilt and Other Wonders
Article #262, November 2017
By Bill Cook

Forests are under constant threat from current pests, and more pests are always on the horizon.  Forest owners and those interested in forests can help reduce negative impacts by learning about forest health issues.
     Oak wilt has been around for at least 75 years.  However, only within the last 15-20 years has the exotic disease really begun to make the news in Michigan, and especially over the last five years.  Although, state and federal agencies have been fighting the disease for over two decades.
     Oak wilt is a fungus that kills the living tissues under the bark.  Once a tree’s transportation system is broken, the leaves quickly wilt and most will fall off the tree.  This usually happens within a few weeks.  The entire tree is killed, not just a part of the tree, especially those in the red oak group (pointy-tipped leaves).
     The fungus enters a tree in one of two ways.  Overland, a group of picnic beetles inadvertently spreads spores while feeding on sap from oak wounds.  Underground, the fungus spreads from tree to tree via root grafts. 
     The overland spread season runs from mid-April to mid-July.  And, that’s a somewhat conservative window.  For the time being, there are no data to suggest expanding that window, but that could change with additional research.  This is important, especially for logging contractors, tree care companies, and crews that maintain utility rights-of-way. 
     For homeowners, this means that avoiding injury to oaks is important.  When wounds do occur, they should be immediately painted-over.  Research has shown that the picnic beetles can find fresh wounds in as little as 10-15 minutes. 
     For current recommendations about oak wilt and disease management, refer to MSU Extension bulletin E3169
     The response to oak wilt depends largely on the environment where the outbreak occurs and the decisions of the property owner.  In wildland situations, woodland owners can treat diseased areas using deep trenching or simply let the disease run its course (neighbors might object).  This treatment should be set-up by a trained person.
     Oak trees in urban and residential environments typically have higher individual value, at least visually, but the situations are usually complicated.  Trenching can be difficult to deploy because of nearby infrastructure and multiple property ownerships.  Chemical injections can be used as preventative treatments, not curative, but they are expensive and must be repeated.   
     Prevention is by far the best option.  Unfortunately, that isn’t always possible. 
     Oak wilt is not the only exotic pest working in our forests and communities.  Nearly everyone has at least heard of the emerald ash borer, first identified in Michigan in 2002.  Beech bark disease is currently running its course through Michigan, some of the last major reserves of the species.  Gypsy moths have been in Michigan for quite some time and are now naturalized, for the most part.  In southwest Michigan, the hemlock woolly adelgid has established itself and there are now quarantines in place.  Geographically close to Michigan are the Asian long-horned beetle and 1000 cankers disease of walnut.  Then if you start looking around, there are even more exotic insects and diseases that pose threats to Michigan trees. 
     Citizens can volunteer to monitor a “sentinel tree” through the “Eyes on the Forest” program.  More observations will increase the likelihood of discovering new exotic infestations while they’re still small and can be eradicated.  Doubtless, the forest environment of the future will be different than that of just a decade ago. 

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TRAILER- This website was created by a consortium of forestry groups to help streamline information about forestry and coordinate forestry activities designed to benefit the family forest owner and various publics that make up our Michigan citizenry. This website is maintained by Bill Cook, Michigan State Extension Forester/Biologist. Direct comments to cookwi@msu.edu or 906-786-1575.

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