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| Oak Wilt Pruning Advisory Update – April 6, 2004 Sap-feeding nitidulid beetles transmit the oak wilt fungus when they fly from sporulating mats produced by the fungus on diseased trees to fresh wounds on healthy trees. Plant pathologists recommend that arborists, tree care professionals and homeowners halt any pruning of oak trees in Minnesota and surrounding states of similar latitude (Wisconsin, Michigan, etc.) during April, May, and June. Pruning cuts result in fresh open wounds that increase the transfer of oak wilt to healthy trees. Oak trees can usually be safely pruned after July 1, in the Lake States. In Minnesota, researchers with the USDA Forest Service monitor the development of oak wilt mats and the flight activity of nitidulid beetles in the spring. As of March 22nd, no new oak wilt mats had been observed and nitidulid beetles were not yet active and flying, indicating that it was still “safe” to prune oaks in the Twin Cities metropolitan area. However, there was a strong odor of the oak wilt fungus in some infected trees, which indicates that mat production could occur rapidly if warm weather continues. Note that weather conditions may differ at other locations, particularly sites farther south, and mat formation and nitidulid activity may be more advanced. |
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