Proper care prevents oak wilt

By Pam Carter - Contributing columnist

Now is the time to trim oak trees to prevent oak wilt disease.

On the heels of the devastation of our beautiful ash trees by the emerald ash borer, everyone realizes we need to become more conscious of the vulnerability of our trees.

One such vulnerable tree is the oak. Strong and stately, perhaps hundreds of years old, the oak appears almost indestructible. However, throughout the Midwest and Texas, many oaks, pruned at the wrong time of the year, die from oak wilt disease.

Oak wilt, caused by the fungus Ceratocystis fagacearum, kills oak trees, according to the OSU Department of Plant Pathology Fact Sheet HYG-3306-09. This fungal pathogen, believed to be native to the United States, was first recognized as an important disease in 1944.

It is necessary to understand the disease cycle and conditions favoring disease in order to prevent its spread. The pathogen spreads from diseased to healthy trees in two ways: over land and under ground. The above-ground spread occurs when beetles travel from a diseased tree, sometimes from a distance of a few miles, carrying the oak wilt fungal spores. The beetles are attracted by the smell of fresh sap to a freshly wounded healthy tree.

The underground spread occurs when the fungus spreads from a diseased tree to a healthy tree through the root systems of trees in close proximity to one another.

All species of oaks are susceptible to oak wilt disease.

Symptoms are typical of wilts, where leaves wither, turn reddish brown and eventually fall from the tree. Other factors, such as drought, construction damage, insect attack, some wood decays and anthracnose can exhibit similar symptoms.

If you suspect oak wilt, it is important to contact the OSU Plant and Pest Diagnostic Clinic at

There are several ways to prevent the spread of oak wilt disease.

Prune oak trees only during the winter months during freezing conditions, when the beetles are not active. Be aware that a few 50-degree days can cause the beetle and the fungus to become active. Or, if an oak is infected in a stand of oaks, trenching can be done around an infected tree to physically sever the actual or potential root contact between the diseased and healthy trees. If pruning is absolutely necessary during the growing season, or if storms create fresh wounds, the wounds can be dressed with latex paint. Although this slows wound healing, it will also deter beetles from landing on the wounds.

Good pruning practices should be followed, such as sanitizing equipment between trees, because fungus can be transmitted through the fungal material residing in sawdust or chips. Be wary about using uncertified tree services. Qualified certified arborists will ensure that a tree is properly pruned.

Any contractor, utility company tree trimmers, county right of way tree trimmers or person who has the opportunity to affect the health of oak trees should be informed of, and follow, proper tree-trimming procedures.

By Pam Carter

Contributing columnist

The writer is a member of Shelby County Master Gardeners.

The writer is a member of Shelby County Master Gardeners.