Proceedings of the Vertebrate Pest Conference

Efforts to establish tree seedlings on sites infested with high populations of pocket gophers (Thomomys spp.) can be futile unless population control measures are implemented. Fumigants are a possible means to reduce pocket gopher populations although the efficacy of fumigants on reforestation sites has been minimal. We conducted a series of experiments to monitor the movement of carbon monoxide through burrow systems and to assess the potential benefits of a blower system. In the first experiment, carbon monoxide was introduced to an artificial burrow system by burning either one or two gas cartridges concurrently or consecutively. The blower was tried at different speeds for varied durations. Carbon monoxide concentration was monitored with sensors that had a detection range from 0 to 5,000 parts per million. Burning the cartridges without the blower was not effective in distributing carbon monoxide. The most effective fumigant dispersal occurred when the blower was used at a low speed for only the period while a cartridge was burning. Burning two cartridges simultaneously was the most effective burn configuration. Results from a second experiment, using vacated pocket gopher burrows instead of an artificial system, were similar to those recorded for the first experiment. Subsequently, we conducted field trials using a blower to disperse carbon monoxide to reduce pocket gopher populations on reforestation sites. These trials did not demonstrate a reduction in pocket gopher activity. We speculate this was because existing burrow plugs prevented the gas from dispersing through the systems or because pocket gophers rapidly blocked burrows when they detected the gas, thus preventing exposure to lethal gas concentrations.