Oak wilt, a disease that affects an oak tree’s water-conducting system, is caused by a fungus transported by a tiny beetle in the spring. Texas A&M Forest Service officials strongly recommend NOT cutting or pruning oak trees from February through June to help prevent the disease. Photo courtesy of Texas A&M Forest Service
The key to controlling oak wilt is prevention, said Texas A&M Forest Service staff biologist Robert E. Edmonson. In fact, he reiterated the point several times when talking about the disease that is a serious threat to Central Texas oak trees.
“And probably the number one thing for preventing oak wilt is don’t prune your oak trees from February through June,” he said. “And when you do prune, make sure you immediately — and I mean immediately — paint over the cut.”
The Texas A&M Forest Service is not an enforcement agency and can only offer support and guidance regarding oak wilt. It created a website, TexasOakWilt.org, with information about the disease and resources available to communities and municipalities.
Oak wilt is caused by a fungus, Ceratocystis fagacearium, that can invade and disable an oak tree’s water-conducting system and cause sudden wilting as well as dropped and discolored leaves. It is often spread from infected to uninfected oak trees by the tiny sap-feeding nitidulid beetle, which is drawn to sweet-smelling substances.
“It’s not a malicious beetle that’s trying to kill oak trees,” Edmonson said. “They’re just opportunistic feeders.”
The nitidulid beetle is about the size of a dot made by a ballpoint pen. It can be found around outdoor food and beverages.
It is also drawn to fungal mats that form during the spring on red oaks (Spanish, Shumard, blackjack, and water oaks). These spore-producing structures let off an odor that smells like fermenting fruit, which attracts the beetle. The fungus is then transported by the beetle to other oak trees, and if any of them have cuts, it’s an opening for oak wilt.
During the hot, dry summers in Central Texas, conditions are much less favorable for the fungal mat-to-beetle transfer. Other insects can transport the disease-causing fungus, but the nitidulid beetle is the predominant insect vector.
Once one oak tree is infected, the disease is difficult to isolate, Edmonson said. Oak trees are connected through their roots, and an infected tree can spread the disease through the shared root system.
“All oaks can get oak wilt,” Edmonson said.
Red oaks, however, are the most susceptible to the disease, and, according to the Texas A&M Forest Service, trees within this group will never survive it.
Live oaks have an “intermediate” susceptibility to oak wilt, but because of the interconnection of roots, the disease can spread quickly among them.
Edmondson encourages people to plant several varieties or species of trees on their property. If oak wilt does infect oak trees in a diverse landscape, the loss of trees won’t be as dramatic.
Also, a diverse landscape is a healthier one and attracts more wildlife, including pollinators, birds, and mammals.