Saving the trees that kill each other - oak wilt

American Forests, Jan-Feb, 1995 by Norah Deakin Davis

Firewood from infected red oaks can contain fungal mats and nitidulid beetles. Every autumn, Jim Rooni and Jay Culver of Austin's Parks and Recreation Department mount an educational campaign advising homeowners to avoid buying logs that come from red oaks. But if a homeowner is unsure of the type of wood being sold, the best thing is to store it under plastic and bury the edges so the beetles cannot escape. Clear plastic should be used rather than black plastic, which allows light to penetrate through rips and puncture holes, showing the insects potential escape hatches.

A final preventative measure for individual high-value trees that have not yet begun showing symptoms is to inject them with a fungicide called propiconazole (trade name Alamo). The rate of success drops dramatically if this treatment is used as a therapeutic measure after a tree has already begun showing symptoms, Culver says. In that case, injection is considered a last resort because the disease simply goes into remission instead of being cured. Also, the fungicide may prolong the life of an individual tree, but it does not kill fungus in the roots and thus does not prevent underground transmittal of the disease.

In 1992 the cost of a fungicide treatment, including labor, for a single live oak 30 inches in diameter ranged from $360 to $450. A 10-inch tree would run about $100. Bill Peters had six trees injected.

The main line of attack is suppression--checking the spread of the disease by isolating affected areas. Trenching machines are used to sever the communal root systems. The disease can still be transmitted by the beetles, but the vast majority of spread is through roots.

"The contractors came in with a big wheel, like they'd use to dig a utility line," recalls Peters. "They went down about three feet by eight inches wide to cut the roots" to separate the intertwining root systems. "They trenched the backyards and sideyards of the house behind me and my neighbor on one side."

The trench was refilled the same day. Roots take eight to 10 years to grow back together, by which time the disease will have run its course. Grass grows back over the trenching scar quickly, but shrubs and flowers have to be replanted.

Trenches for containing oak wilt average 2,000 feet in length--nearly half a mile. "Austin has shallow soils, so a rock saw has to be used in many cases, and the cost can run as high as $8.80 a linear foot. When the path reaches underground utilities, water or sewer lines, fences, or sprinkler systems, the trench has to be dug by hand. When it crosses streets or driveways, it has to be refilled with concrete.

The red tape can be daunting (involving some 31 steps for planning the project and obtaining funds), and the effort and cost are beyond the reach of individual home-owners. To stop this disease, people have to cooperate with their neighbors--whether they like them or not. Austin's parks department works with neighborhood associations to walk them through the bureaucracy.