Oak Wilt in the Live Oaks

The live oaks that give Oak Hill its name grow in dense groves, and in Central Texas a grove is usually one connected organism. Escarpment live oaks send out roots that graft onto their neighbours' roots, so water, sugars and disease all move freely between trees that look separate above ground. That is why oak wilt has been so destructive here. The fungus clogs the water-conducting vessels of an infected tree, and then travels underground through those grafted roots at roughly seventy-five feet a year, killing outward from a centre in a widening circle. It has now been confirmed in more than seventy Texas counties, with the Hill Country at the heart of it. The oaks themselves can be centuries old, which is part of what makes the loss permanent on any timescale that matters to the people watching it. The second route is overland. Sap-feeding nitidulid beetles pick up spores from fungal mats that form under the bark of dead red oaks and carry them to fresh wounds on healthy trees. That is why the Texas A and M Forest Service asks landowners not to prune oaks between February and June, and to paint every cut immediately whatever the season. The standard defence is a trench, cut four or five feet deep by a rock saw a hundred feet or more beyond the last symptomatic tree, severing the root grafts ahead of the infection. Along this stretch of US 290 the evidence is easy to read from the car: a mott of live oaks with a hollow of grey standing trunks at its centre, and somewhere beyond it the trench line where somebody tried to stop it.