Don’t prune oaks from April-Nov.

Q. I know you said earlier this year to hold off pruning oak trees until fall. Is there still a danger right now of infection from that insect?

Jack from Canfield

A. The short answer is no, because of the possibility of the tree getting infected with oak wilt.

Oak wilt is a devastating fungal disease that is spread to oak trees two ways. The first is by common roots. OSU experts estimate that 90 percent of new infections come via root grafts of infected trees. That is, oak tree roots graft together, allowing the transfer of the fungus via the vascular system of the tree.

The second way the disease spreads is why we don’t prune oaks during the growing season.

Beetles transmit the oak wilt fungus by getting the sticky spores of the fungus on their bodies while on infected trees. Then, they fly to other oak trees where they feed on the oak tree’s sap. The sap is usually dripping where a branch has broken off the tree, creating an open wound – or where you have pruned the branch. Squirrel damage for nest making is another way fresh wounds are created during summer months.

So you should not prune red oaks during the growing season to keep the number of wounds to a minimum that nature causes. Making pruning cuts only leaves your trees more susceptible to disease transmission from beetles carrying the fungal pathogen.

A common myth relating to oak wilt disease is that it only affects red oaks. While not as susceptible, white oaks can get the disease. They are affected differently and are slower to show symptoms. Thus, we suggest avoiding the pruning of any oaks from April through November.

Details and photos of the disease here in Ohio are on our factsheet at http://go.osu.edu/oakwilt

When it comes to pruning other trees during the summer, it is generally OK to do so. This is especially true when branches get broken off or damaged due to storms.

Doing a good job pruning by avoiding leaving stubs or cutting too close to the trunk will go a long way in maintaining tree health.

When it comes to wounds, we do not recommend covering, painting or spraying tree wounds unless it is an oak tree during the growing season.

Learn more about pruning and caring for tree wounds at: http://go.osu.edu/treewounds.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office hotline at 330-533-5538 to submit your questions. Regular clinic hours are 9 a.m. to noon Mondays and Thursdays.