Springtime Means Stop Pruning Oak Trees
(compiled, May 2, 2015)
The experts at MSU Extension are advising people to avoid the spread of Oak Wilt by not pruning their Oak trees now that it is springtime. According to Bert Cregg, Michigan State University Extension, Departments of Horticulture and Forest:
“Oak wilt is an aggressive disease that affects many species of oak (Quercus spp.). It is one of the most serious tree diseases in the eastern United States, killing thousands of oaks each year in forests, woodlots and home landscapes. Oaks in the red oak group, distinguished by oak leaves with pointy lobes, are much more susceptible to the disease than white oaks, distinguished by oak leaves with rounded lobes. However, all oaks can be affected.
Oak wilt is a vascular disease that interferes with the tree’s ability to move water from its roots to its leaves. In red oak trees, the disease progresses quickly and trees may be defoliated within weeks of infection.
Oak wilt spreads by two means: overland spread and local spread. In overland spread, sap beetles carry spores from dead trees and infect new trees. Normally a tree’s protective bark is sufficient to protect it from infection, but the beetles are strongly attracted to fresh branch wounds, either from broken branches or pruning cuts, which allow the spores to infect the tree. Because of this, it is critical that homeowners and arborists do not prune oaks from April 15 to July 15 in Michigan. Oak wilt can also spread overland by moving wood. Michigan State University Extension advises to avoid moving wood from trees killed by oak wilt.
In local spread, once a tree is infected with oak wilt, the infection can spread to neighboring trees via root grafts. Therefore it is important to isolate root systems of infected trees, usually by soil trenching or removing stumps.”
For more information on oak wilt, see:

• Michigan Oak Wilt Pest Alert, Michigan DNR
• How to Identify, Prevent and Control Oak Wilt, USDA Forest Service

Dr. Cregg’s work is funded in part by MSU’s AgBioResearch.
The original article was published by Michigan State University Extension. For more information, visit http://www.msue.msu.edu. To have a digest of information delivered straight to your email inbox, visit http://bit.ly/MSUENews. To contact an expert in your area, visit http://expert.msue.msu.edu, or call 888-MSUE4MI (888-678-3464).