Prevent oak wilt by eliminating pruning wounds in spring and summer

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Oak wilt caused by the fungal pathogen Ceratocystis fagacearum can kill large northern red oak trees in one year from time of infection. Infected trees can also serve as conduits of infection as the root grafts that naturally form in dense oak plantings allows the fungus to move from dying infected oaks to nearby uninfected oak trees.

Overland, the greatest source of infection comes from sap beetles (aka picnic beetles; nitidulids). These small black beetles with red spots can spread the fungus long distances (miles). Oak trees bleeding sap in April, May and June are at greatest risk for being visited by the sap beetles. The bleeding sap attracts the beetles, and if some of the beetles are carrying the fungal pathogen, they can inoculate the trees.

Pruning wounds, wind damage, construction damage or any damage that allows the oak trees to bleed sap during the high-risk months needs to be attended to immediately. Most importantly, don’t prune in April, May and June, and if wounds do occur, paint the wounds as soon as possible with tree sealer. This should reduce the attraction of the wounds to the beetles

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