Proceedings of the Vertebrate Pest Conference

Intermountain alfalfa fields are ideal habitat for burrowing rodents like pocket gophers and Belding’s ground squirrel, due to an alfalfa stand life of at least 5 to 7 years and sprinkler rather than flood irrigation. Current control measures are only marginally effective and are expensive or extremely labor intensive, so many alfalfa producers have no rodent management program whatsoever. A new device called the Pressurized Exhaust Rodent Controller (PERC) was developed to control burrowing rodents using an internal combustion engine to generate and pressurize carbon monoxide that is injected into the burrow system using multiple hand-held probes. Field trials were conducted in April and May 2006 to evaluate the effectiveness of this device for controlling both pocket gophers and Belding’s ground squirrels in Siskiyou County, CA. An additional gopher control study was conducted in October 2011 to evaluate a newer version of the PERC device. Gopher studies were conducted in three commercial alfalfa fields and ground squirrel studies in an alfalfa field and a dryland range field. The PERC unit was used to inject exhaust fumes into the gopher burrow system. Approximately 24 hours after treatment, the gopher burrow systems were opened. Control was estimated by assessing the number of burrow systems that remained open the following day. Using the open-hole index technique to assess gopher activity, control efficacy was calculated to be 61%, 63%, and 45% for the two 2006 studies and the 2011 study, respectively. In the Belding’s ground squirrel studies, the hand-held probes were inserted into the open burrows and the burrow opening closed with soil prior to injecting the carbon monoxide exhaust. Control was assessed by determining the percentage of burrow systems that were reopened the day after treatment. Control efficacy for the two squirrel studies was calculated to be 81% and 71%. These preliminary results suggest that the injection of pressurized exhaust in gopher and squirrel burrow systems may be effective as part of an integrated vertebrate pest management program, but additional research is needed to further define the parameters required for effective control.