Give oaks care they deserve

Right off the bat I want to suggest that any major work done on oak trees is always best when it is under the supervision of an arborist certified by the International Society of Arboriculture. It’s even better if that ISA-certified arborist has a plant pathology degree or has been through the additional training and certification in the specialty of dealing with oak wilt.

Let me give you a few generalities.

• Oak wilt is caused by the fungus Bretziella fagacearum.

• According to the website of the Ohio Chapter of the I.S.A., oak wilt was first reported in Wisconsin in the early 1940s. Subsequently it was reported in Texas in the early 1960s. It is now reported in 24 states.

• Oak wilt is spread in two ways. During the growing season, particularly between mid-February and mid-July in Texas, it is spread via fresh, open wounds recently made into the wood of the trunks and branches. Carried by a beetle, the fungus can invade pruning cuts that are left unsealed, but it can also get its start through recent damage such as broken branches, scuffed bark (mowers, line trimmers, etc.), and other exposed green wood.

Further complicating the problem greatly, oak wilt is also spread by root grafts from an infected tree to a formerly healthy tree. This is how expansive groves of live oaks are lost in the Hill Country.

• All species of oaks are susceptible to some degree, but the red oak group (pointed lobes on the leaves) is more susceptible than the white oak group (rounded lobes). The Texas A&M Forest Service lists live oaks as being intermediate in susceptibility, but they say the disease is epidemic in Central Texas because of those interlocking root masses.

• When hiring a tree crew, be sure the details are outlined by certified arborists, and be certain that their crew leader is schooled in oak wilt, its proximity in your neighborhood, and proper techniques of pruning and caring for oaks.

• All pruning cuts into green tissue should be sealed in the spring months. While arborists and foresters no longer recommend use of pruning sealants across the board with other types of trees, with oaks, pruning paint or latex paint should be applied to each wound immediately after each cut is made. The beetles that carry the fungus seem to be able to detect fresh cuts almost as soon as they’re made.

Texas Oak Wilt
The Texas Oak Wilt Partnership has been formed between the Texas A&M Forest Service and the Forest Health Protection branch of the USDA Forest Service.

You will find useful information at the coalition’s website. (https://texasoakwilt.org) This information is geared toward homeowners across the state of Texas in general. Local certified arborists skilled in dealing with oak wilt in your specific area may fine-tune their management procedures compared to these more general guidelines.

Either way, before you start pruning your oaks or hiring someone else to do the work for you, you would be wise to check out the information on that website.

• This page from the organization’s website will be invaluable in identifying oak wilt. It also gives instructions on collecting and sending samples to the Texas A&M Plant Disease Diagnostic Laboratory along with the form that must accompany the submission.

• Here is the coalition’s information on managing the disease. Almost all of this needs to be left to certified arborists trained in oak wilt issues.

• If you’d like a 1-page “quick guide” you can print and share with others, this page from the coalition’s website tells the whole story in a nutshell.