Oak Wilt

Oak Wilt Scenarios:

  1. This past July, Integrity Tree Services received a phone call from a customer requesting one of our arborists to have a look at their red oak tree.  She informed us the mature red oak had been pruned in late May, and suddenly it was rapidly dropping leaves.  This is a sign of oak wilt.
  2. A customer called last September wanting his black oak tree examined. A storm had come through his neighborhood and broke a massive limb off the tree.  He was very knowledgeable on oak wilt and knew the situation was precarious.  We were able to save the tree.

Oak wilt (Ceratocystis fagacearum) is an infectious fungal disease, which causes rapid death in oak trees and in certain oak families, in a matter of weeks. It can be transmitted by sap beetles (Nitidulidae) as well as oaks sharing roots underground, commonly called root grafts (Brown-Rytlewski, 2007). Also, it may occur when an oak is pruned in the spring or summer months.

During the warm months of the year, sap beetles are actively feeding on tree sap. The beetles find their meals by their strong sense of smell and are lured in, particularly to the smell of sap from a freshly cut oak (Johnson & Lyon, 1987). If an oak is pruned during the spring or summer months of the year, it is an open invitation for beetles potentially carrying fungal spores. Once a beetle finds a fresh wound, it can contaminate a healthy oak with the oak wilt fungus. The results are the vascular system clogging up causing leaves to turn tan, brown or bronze, and to fall rapidly from the tree.

The sap beetles lay their eggs in dead oaks and can often emerge contaminated with fungal spores (Johnson & Lyon 1987). The spore mat of the oak wilt fungus is commonly called a pressure pad. The pressure pad grows underneath the bark of an oak already infected with oak wilt from the previous year. This spore mat creates pressure on the bark and causes it to split. The beetles cannot resist the sweet smell of the fruiting body and will be drawn to it (Sinclair and others, 1987).

Not all methods of contracting the oak wilt disease are due to improper pruning. As described in scenario 2, branches break in strong winds or storms.

Not all oaks are extremely susceptible to oak wilt. Oaks in the red oak family (oaks with pointed lobes) are the most susceptible. Once infected with oak wilt, a mature, healthy red oak tree can die within the first month of contraction (Johnson & Lyon, 1987). Once a red oak contracts oak wilt, it is certain to die. Nothing can save a red oak tree after it is infected. Oaks in the white oak family (oaks with rounded lobes), however are much more resistant to the disease. The disease in white oaks is very slow to progress and white oaks can live with oak wilt for years (Johnson & Lyon, 1987).

It is very common to hear of heart breaking stories where a homeowner will try to save money by hiring a less-expensive, non-reputable tree company to prune their landscape trees. If an oak tree is to become infected due to improper pruning, all other oak trees on the property, as well as all oaks in the neighborhood, are at risk for contracting oak wilt.

We are approaching the autumn months, which is a good time to receive an estimate on getting your oaks pruned. After receiving an estimate, we will then schedule the tree work to occur in late fall or winter. If it is getting too late in the winter season and spring is near, we will wait until the following fall or winter before any tree work on oaks is done. We will not risk trimming your oaks too close to springtime.

Please email kimb@integritytree.com if you’re interested in receiving more information on oak wilt.