Large-scale spread of oak wilt is controlled by cutting trenches around an entire oak wilt center, severing the roots and stopping root transmission. Oak wilt can "break out" and spread to trees outside if the trench was installed too close to infected oaks or if it was not deep enough to sever all the roots. Most trenches are cut to a depth of four or five feet with a rock saw, backhoe and manual labor.
Trench installation: cut and backfill
"Trenching" is a misnomer because the oak wilt suppression trenches are filled in immediately after the roots are cut. The material that comes out is compacted back into the trench and the landscape is restored.
Trench 100+ feet beyond infected oaks
The Texas Forest Service recommends installing trenches a minimum of 100 feet beyond symptomatic oaks. When a trench is installed too close to infected trees, oak wilt often appears outside the trench within weeks. Oaks that appear healthy may be in the earliest stages of infection, so there should always be a group of non-symptomatic oaks between infected oaks and the trench line. Trenches should be placed beyond properties where all oaks have been treated with fungicide.
Trenching in urban neighborhoods
Cutting a four-to five-foot deep trench in urban areas and residential neighborhoods is mighty tough work. An eight-foot wide, 24-foot long rock saw is difficult to maneuver in tight spots. A backhoe, pick, shovel and lots of muscle are used to dig the trench to a four-foot minimum depth where the rock saw won't fit. Care must be taken to avoid cutting utility lines. In areas where limestone is close to the surface, it must be jackhammered out with a hoe ram attached to the backhoe.
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