Now that it’s April, experts say don't prune oak trees until after July…if you want to keep them safe from the oak wilt pathogen. Oak wilt is a deadly fungus that gets transmitted through tiny sap beetles.
DNR Forest Health specialist Brian Schwingle says oak wilt works in a similar way as Dutch elm disease, which devastated North American elm populations in the 20th century. Both are fungal diseases spread through beetles. But Schwingle says out of the two, oak wilt is much easier to prevent.
“Because the beetles that carry Dutch elm disease actively drill into the tree – they’re bark beetles. Whereas with oak wilt, those beetles need an open wound to spread the disease.´
An open wound results from pruning or other kind of damage. That’s why the DNR is asking the public not to prune oak trees between April and July…when they’re most vulnerable to the disease.
“We don’t see oak wilt moving overland nearly as much outside of that period, April through July, because the conditions just aren’t right. It’s either too dry for the fungus…or the beetles, that’s just not the period of the year when they’re most abundant.”
Oak wilt is common in the southern part of the state. Once established it can also spread underground through root systems. But it has only been found in five locations in Oneida and Vilas counties…and Schwingle says at least three of those could have been prevented by not pruning during the growing season.
Signs of oak wilt include withered leaves or a tree rapidly losing all its leaves in a short span of time. If you think you have a tree that could have oak wilt, you should report it to the DNR.