U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

August 2005


A pre- and post-monitoring study was conducted of the potential use of capsicum oleoresin as an in-soil repellent for northern pocket gophers (Thomomys talpoides). Pocket gophers were captured in irrigated alfalfa (Medicago sativa L), affixed with radio transmitters, and monitored daily for location. Six plots (4.87 × 4.87m) each were randomly assigned to capsicum oleoresin and soybean oil treatments; these were set up based upon the centers of initial core areas of gophers. Mean (±SD) volumes of capsicum oleoresin and water and soybean oil and water mixtures (10 + 90 by volume) dispensed onto plots equaled 178.5 (±4.7) and 175.7 (±14.0) liters, respectively. Movements (m) of the radio-transmitted gophers from plot centers were computed for four daily readings (i.e., 0801–1000, 1101–1300, 1501–1700 and 1801–2000 h). Spectrophotometric analysis of soil samples from capsicum oleoresin plots validated the presence of capsicum on plots and the absence of capsicum on placebo- and off-plot locations. Analysis of variance for movement distances of gophers yielded a Date main effect [F(11, 103) = 2.08, P ≤ 0.03] and a Date × Reading (time) interaction [F(32, 299) = 3.21, P ≤ 0.01]. Results showed that gophers were located farther from plot centers for the 0801–1000 and 1501–1700 h telemetry readings for ≤3days postchemical application—a probable ‘disturbance’ effect rather than a chemical-induced avoidance. In a prior laboratory study, capsicum oleoresin and soil treatments of 1.5% w/w capsicum caused nearly a 50% decrease in soil contact time by gophers relative to placebo-exposed control animals. This implies that procedural variables warrant revision before abandoning this approach. The potential for soil insertion of repellents as a technique for expelling pocket gophers from territories and some methodological changes for future research of the technique are discussed.