Preliminary Field Evaluation of a New Formulation of Rozol ( Chlorophacinone ) Bait against Pocket Gophers in Colorado

Mountain pocket gophers (Thomomy's talpoides) and plains pocket gophers (Geomys bursarius) are a problem to rangelands in Colorado. A new chlorophacinone (50 ppm) pelleted bait was applied to active burrow systems by hand baiting. Efficacy on the Geomys plot was 100%, while 94.73% of the Thomomys were controlled with the product. Introduction Pocket gophers, of the family Geomyidae, are indigenous to the western hemisphere from central Alberta to Panama (Turner et al. 1983). The mammalian group is represented by 8 genera, 30 species, and about 300 subspecies (Hall and Kelson 1959). Of the 4 species of pocket gophers found in Colorado, the northern pocket gopher (Thomomys talpoides) is the principal species found on mountain rangelands. Others include the southern pocket gopher (T. umbrunus), plains pocket gopher (Geomys bursarius) and the yellow-faced pocket gopher (Pappageomys castanops). According to Hansen and Reid (1973), the 4 species are almost entirely allopatric in distribution, but in some areas, 2 species do overlap. Although interspecific intolerance is evident (Vaughan 1967), similar ecological requirements apparently prevents sympatric distribtuion and suggests intense interspecific competition (Miller 1964). Pocket gophers (Thomomys spp.) are considered among the most serious problems in damaging conifer seedlings and hampering reforestation efforts in the western U.S. (Tunberg et al. 1984, Black 1970, Barnes 1973). As a result of pocket gophers feeding on seedling roots below ground surface, we have observed cases of up to 80% tree mortality in 1-year old planted tracts in Idaho. Government agencies, such as the U.S. Forest Service, are now required to contract for gopher control in clearcut or burned areas before planting seedlings. Failure to consider gopher control can often result in a waste of time and money paid to contractors. On rangelands, pocket gophers play an important role in burrowing and pushing soil to the surface, thus promoting vertical cycling and mixing of soil constituents. Richens (1966) estimated that 75 gophers per hectare, an average on mountain rangelands, may move 38 tons of soil in one year. However, where abundant, gophers can cover up to one-fourth of the ground surface with mounds and castings in 1 year (Turner 1973). Grinnel (1923) observed, however, that coverage of 5-15% is more common. During the late summer and early fall, gophers tend to burrow more extensively in search of underground food During this time, caching of plants tends to increase and continues even after snowfall. Casting may cover more ground area than mounds.