Protect Oak Trees from Oak Wilt

April 2, 2017 lawanda Newspaper Columns

        Before European settlement, most of Winnebago County was an oak savanna.  Oak trees were the main component of the plant community, but their density was low enough that grasses and other vegetation could thrive.  For a variety of reasons, today the oak savanna is one of the rarest plant communities on earth.

        While most of us don’t own enough acres to help restore the oak savanna, many stately old oaks still grace our cities and rural areas and we should do everything we can to protect and preserve them.           The Wisconsin DNR advises us to protect oak trees from a fungal disease called oak wilt by not pruning oaks from April through July.  Oak wilt is a fatal disease that affects oaks in the red oak group – those with pointed leaf edges – most easily.  Oaks in the white oak group – those with rounded leaf edges – are less susceptible but can be infected.  The disease has been found in Winnebago County.

        The oak wilt fungus blocks the paths inside the tree where water moves.  When water can’t reach the top of the tree, the leaves wilt and drop off and the tree dies.              

        The disease spreads several ways. 

        Above ground, pruning or any tree damage that exposes live tree tissue can attract beetles that carry oak wilt spores within just 15 minutes!  Tree paint and wound dressing are no longer recommended for most pruning cuts or wounded tree surfaces, but if your oak tree is damaged or you are forced to prune between April and July, an immediate light painting of the cut or wound will help protect against oak wilt.  Take note:  immediate means right away.  Cut.  Paint.  It doesn’t mean make the cut and then go look for the paint, or take a break, or cut five other branches first.

        Where do these beetles get the disease to start with?  They are attracted to the sweet smell of fungal mats growing under the bark of oaks that have already died of oak wilt.  The mats grow and force the bark to crack open and the beetles swarm to feed on the sap.  The fungus gets on their bodies as they feed.  When a healthy oak has a fresh wound, they flock to the sap flowing from that tree and spread the fungal spores.

        Once a tree is infected with the fungus, the disease can spread to nearby oaks whose roots have become interconnected underground.

        A final way the disease spreads is by moving contaminated firewood logs year-round.  It is difficult to tell whether firewood is contaminated just by looking at it.  Fungal mats may be hiding under the bark.  So don’t transport oak wood.

        The DNR website has much more information regarding determining whether your oak has wilt, what to do if it does, how to prevent the spread to other oaks below ground, and safely harvesting the wood of an infected tree.  Please see http://dnr.wi.gov/topic/ForestHealth/OakWilt.html.  Additional information can be found at http://learningstore.uwex.edu/Assets/pdfs/G3590.pdf.

Pests/Weeds/InvasivesTrees and Shrubs


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