State of Michigan

04/14/2021 | Press release | Distributed by Public on 04/14/2021 16:11

Help prevent the spread of oak wilt: Avoid pruning or wounding oak trees between April 15 and July 15

Oak trees have a reputation for being mighty, but these majestic trees need our help in spring and early summer to prevent the spread of a microscopic killer.

From April 15 to July 15, oak trees are at high risk for oak wilt, a serious fungal disease that can weaken white oaks and kill red oak trees within weeks of infection. During this time of year, flying beetles can carry oak wilt fungus spores from tree to tree and the fungus can infect trees through wounds left by pruning or storm damage.

'The guidelines against pruning oak trees during this time can help prevent the spread of the disease,' said James Wieferich, forest health specialist in the DNR's Forest Resources Division.

The fungus can move from an infected oak to neighboring oaks through root grafts. Depending on tree size, adjacent oaks may be connected to other trees, or grafted, through root systems. Roots of large trees can reach 100 or more feet. Left untreated, oak wilt will continue to move from tree to tree, killing more red oak over an increasingly larger area. As more trees die from oak wilt, more fungal spores are produced, which allows the beetle to carry infection to new locations. Trees in the white oak family are more likely to survive an infection because they are capable of compartmentalizing the fungus.

Oak wilt was first identified in Michigan in 1951 and this invasive species now is widespread across the state. An invasive species is one that was introduced to Michigan's environment from elsewhere and can cause harm to the environment, economy or human health.