Efficacy of a two-ingredient fumigant on Richardson's ground squirrel

In July 1981, efficacy data were obtained on a new two-ingredient gas cartridge by field testing against Richardson's ground squirrels (Spermophilus richardsonii) in a sagebrush-rangeland pasture. The gas cartridge contained 97 g of a sodium nitrate (65%) and charcoal (35%) mixture and upon ignition generated mainly carbon monoxide with a small quantity of carbon dioxide. We live-trapped 53 (24 male and 29 female) ground squirrels, equipped each with a 164 MHz radio transmitter, and then released each at the point of capture. Later we located each ground squirrel and treated its main burrow and all burrows within 3 m by inserting ignited gas cartridges. After treatment the location of each radio-equipped ground squirrel was plotted. Ground squirrels showing no movement were presumed dead; death was confirmed by burrow excavation. Success rate was 84% as 41 of 50 (18 males and 23 females) died (82%) and 8 survived (16%). The radio transmitter on 1 (2%) failed immediately after treatment. Efficacy was estimated at 83.7%, which exceeds the 70% minimum standard established by the EPA. Thirty-eight ground squirrels died in burrows at depths ranging from 7.6 to 132.1 cm (mean = 74.7 ± SE 5.2 cm), and 3 died in nests at depths ranging from 94.0 to 182.9 cm (mean = 133.0 ±SE 26.2 cm). Seven of the eight survivors were retrapped. Factors contributing to survival are discussed, including soil porosity and moisture content, as well as squirrel body weight. Recommendations for further testing are presented

CHLOROPHACINONE BAITING FOR BELDING’S GROUND SQUIRRELS

The efficacy of using 0.01% chlorophacinone on steam-rolled oat (SRO) groats applied in CA alfalfa by spot-baiting/hand baiting around burrow entrances (~11.5 g) to control free-ranging Belding\u27s ground squirrels (Spermophilus beldingi) were compared in 6 randomly assigned square treatment units (TUs). Four TUs were given the rodenticide and 2 treated with placebo bait. Each TU was a 0.4 ha square surrounded by a similarly treated 5.5 ha square buffer zone. Baits were applied on May 13 and re-applied, on May 20 and May 22, after 7 days of un-forecasted cool wet weather greatly reduced their above ground activity. Pesticide (EPA SLN CA-890024) efficacy was calculated as % reduction (PR) of ground squirrels on each TUs measured directly by visual counts (VCs) and indirectly by active burrow counts (ABCs). VCs and ABCs provided mean PRs that met US EPA\u27s 70% minimum standard efficacy threshold for field rodenticides (x = 73.5%, SD ± 13.3; x = 80%, SD ± 6.2, respectively). ANOVA results of the PRs were highly significant (F = 29.72, df 1/4, p = 0.0055 and F = 72.92, df 1/4, P = 0.001, respectively). All carcasses (38) located above ground were analyzed for pesticide and 80% had detectable levels in whole animals (x = 0.1131 ppm, SD ± 0.0928). Suggestions to improve the pesticide’s efficacy and lessen its potential nontarget hazards were discussed

Safe efficacy of three strychnine alkaloid bait concentrations for hand-baiting control of plains pocket gophers

In November 1990, field efficacy studies using milo baits formulated with 0.35%, 0.75%, or 1.30% strychnine alkaloid were compared to a placebo (0.0% strychnine) for controlling plains pocket gophers (Geomys bursarius) near Pleasanton, Texas. These data were required by the US Environmental Protection Agency (EPA) as partial fulfillment for the maintenance of the rodenticide registrations of the US Department of Agriculture. Each of four treatment units (TUs) within a block (2) was randomly assigned one of the four baits. Within each TU, 15 gophers were captured (balanced roughly for gender) and instrumented with radio transmitters. Following a pretreatment acclimation averaging 4.1 days, bait (4 g) was placed in active pocket gopher burrows by hand-baiting. Pocket gopher mortality was measured by monitoring the fate of radio-equipped pocket gophers (n=123) both pretreatment and post-treatment. Lack of gopher movement on two consecutive days indicated death, and the carcass was retrieved. Strychnine mortality was based on chemical analyses of carcasses, and it occurred in 0.0%, 66.7%, 96.3%, and 89.7% of gophers from the 0.0%, 0.35%, 0.75% and 1.30% TUs, respectively. Natural mortality was 7% on the placebo TUs. All three strychnine treatments provided significantly increased mortality over the placebo (P\u3c0.0001) using Fisher\u27s exact test for paired comparisons. A difference in gopher mortality occurred between the 0.32% and 0.77% strychnine treatments (P=0.003), but not between the other comparisons (0.32% vs 1.30%, P=0.18 and 0.77% vs. 1.30%, P=0.24). Gopher carcasses recovered post-treatment indicated 68 of 86 (79.1%) had strychnine alkaloid residues. The non-target strychnine hazard (using least squares means) by treatment were 4.85 ppm (0.35%), 8.04 ppm (0.75%), and 9.47 ppm (1.30%). Carcass residue differences were not detected among strychnine treatments (F=2.48, df=2,3, P=0.23). Fortunately, non-target exposure was greatly decreased because all carcasses with strychnine residues were recovered underground at a mean depth of 0.51 m (SE=0.027, range 0.15–1.17 m). Placebo-baited TUs had 27 survivors and 2 deaths from unknown causes. None had detectable strychnine levels. No non-target mortalities were documented during carcass searches and radio-tracking activities

EFFICACY OF A TWO-INGREDIENT FUMIGANT ON RICHARDSON\u27S GROUND SQUIRRELS

In July 1981, efficacy data were obtained on a new two-ingredient gas cartridge by field testing against Richardson’s ground squirrels (Spermophilus richardsonii) in a sagebrush-rangeland pasture. The gas cartridge contained 97 g of a sodium nitrate (65%) and charcoal (35%) mixture and upon ignition generated mainly carbon monoxide with a small quantity of carbon dioxide. We live-trapped 53 (24 male and 29 female) ground squirrels, equipped each with a 164 MHz radio transmitter, and then released each at the point of capture. Later we located each ground squirrel and treated its main burrow and all burros within 3 m by inserting ignited gas cartridges. After treatment the location of each radio-equipped ground squirrel was plotted. Ground squirrels showing no movement were presumed dead; death was confirmed by burrow excavation. Success rate was 84% as 41 of 50 (18 males and 23 females) died (82%) and 8 survived (16%). The radio transmitter on 1 (2%) failed immediately after treatment. Efficacy was estimated at 83.7%, which exceeds the 70% minimum standard established by the EPA. Thirty-eight ground squirrels died in burrows at depths ranging from 7.6 to 132.1 cm (Χ̅ =74.7 ± SE 5.2 cm), and 3 died in nests at depths ranging from 94.0 to 182.9 cm (Χ̅ = 133.0 ± SE 26.2). Seven of the eight survivors were retrapped. Factors contributing to survival are discussed, including soil porosity and moisture content, as well as squirrel body weight. Recommendations for further testing are presented

EVALUATION OF ACROLEIN AS A FUMIGANT FOR CONTROLLING NORTHERN POCKET GOPHERS

Baker Performance Chemical Incorporated entered into a cooperative agreement with the National Wildlife Research Center to evaluate acrolein as a fumigant for controlling northern pocket gophers (Thomomys talpoides). In October 1996, a 44.5 ha (110 acre) irrigated alfalfa hay field was selected as the study site in Franklin County, Washington. Eight treatment units (TUs), six fumigated and two control, were established on the study site. On the six fumigated TUs, 58.9% of the sample plots were inactive, whereas, all sample plots (100%) on the two control TUs were active. The 58.9% mean reduction in pocket gopher activity on the six fumigated TUs was below the minimum efficacy standard of 70% established by the Environmental Protection Agency (EPA 1982). Possible reasons for the pocket gophers surviving the acrolein treatment are discussed

EFFICACY OF TRIMETHAC ARB AS A SMALL MAMMAL REPELLENT IN NO-TILL CORN PLANTINGS

Trimethacarb (2,3,5-trimethylphenyl methycarbonate) was evaluated as a mouse repellent in no-till corn plantings. Two studies were conducted. One involved an early spring planting and included 5 treated and 5 control plots. The second involved a late spring planting and included 3 treated and 3 control plots. Species composition and relative abundance of small mammals were determined for each plot by trap and release before treatment. On the 10 early spring plots, species composition was 85% prairie voles (Microtus ochrogaster). 14% deer mice (Peromyscus spp.). and 1% house mice (Mus musculus\u27). On the 6 late spring plots, species composition was 66% prairie voles, 28% deer mice, and 6% house mice. Trimethacarb (15% by weight) was applied in a 15-20 cm band on the ground surface over the planted corn seed at a maximum rate of 9.2 kg/ha. Corn seeds consumed by small mammals and intact corn sprouts were counted when the corn was approximately 10 cm tall, or about 17 days after planting. At harvest, the numbers of corn stalks and yield in kg per ha were estimated. In the early spring planting, mice consumed a total of 657 and 755 seeds on the 200 sampling sites (treated and control plots, respectively). In the late spring planting, mice consumed a total of 122 and 87 seeds on the 120 sampling sites (treated and control plots, respectively). Differences between the mean numbers of seeds consumed by mice on the treated and control plots were not statistically significant in either planting. In the early spring plantings, a total of 1,784 and 1,641 intact sprouts were present on the 160 sampling sites (treated and control plots, respectively). In the late spring plantings, a total of 1,267 and 1,114 intact sprouts were present on the 120 sampling sites (treated and control plots, respectively). Differences between the mean numbers of intact sprouts on the treated and control plots were not statistically significant in either planting. The average numbers of stalks per ha at harvest for the early spring planting were 42,230 and 31,604 (treated and control plots, respectively); estimates for the late spring planting were at 42,929 and 40,597 (treated and control plots, respectively). Differences between the numbers of stalks on the treated and control plots were not statistically significant for either planting. Average yield for the early spring planting was 8492 kg/ha and 6267 kg/ha (treated and control plots, respectively); and for the late spring planting was 6618 kg/ha and 6831 kg/ha (treated and control, respectively). There was no statistically significant difference in kg/ha between treated and control plots for either planting. These results indicate that trimethacarb is not an effective mouse repellent in no-till corn plantings

Population Reduction of Richardson\u27s Ground Squirrels Using a Brodifacoum Bait

On 6 study plots (3 treated and 3 control of 2.47. acres--1 ha), we evaluated the efficacy of a 50 ppm brodifacoum grain bait on Richardson\u27s ground squirrels (spermophilus richardsonii Efficacy was measured by 3 methods: (1) radio-telemetry - 22 ground squirrels were live trapped on each treated plot and equipped with radio transmitters, (2) mark-recapture - by mark-recapture sampling methods and the computer program entitled CAPTURE, and (3) Tanaka\u27s formula - by using only marked survivors retrapped posttreatment. Treatment began the day following the pretreatment trapping period by systematically baiting each burrow entrance with approximately 16-19 g of bait. Overall efficacy of brodifacoum when measured by radio-telemetry was 98.1$, by mark-recapture 96.8% (SE x,1.5%) and by T-naka\u27s formula 99.1% (SE t 1.5%). Ground squirrels dying above ground varied between 18 and 64 among the 3 treated plots. The percentage of marked ground squirrels recovered dead above ground on the treated plots averaged 14.6% (range 6.8-24.5x). Non-target mortality on the treated plots included 3 vesper sparrows (Pooecetes gramineus and a white-tailed jackrabbit (L-enns t-ownsendi). Brodifacoum residues were 0.76 ppm for 1 vesper sparrow and at the level of detection (0.50 ppm) for the remaining vesper sparrows and the jackrabbit. The 50 ppm brodifacoum treatment tested on Richardson\u27s ground squirrels showed greater efficacy with less variability than zinc phosphide in previous studies on the same species

Seasonal marking efficacy of Dupont oil blue A dye on steam-rolled oat groat baits for valley pocket gophers

We examined if Valley pocket gophers (Thomomys bottae) exhibited a seasonal preference for consuming steamed-rolled oat (SRO) groat bait treated with 1.6% Dupont oil blue A (fat-marking dye). Field tests were conducted in California alfalfa fields during winter, summer, and fall, and in walnut orchards during winter and summer. Five treatment units (TUs) were established each with 60 burrows for each season and habitat studied during 1997–1999. SRO groat marker bait (4 g) was placed inside each active burrow. All bait sites were re-opened about 96 h later and examined for the presence (all or some) or absence of bait. The average bait site disturbance after 4 days of baiting was 78.2%. Traps were used to capture gophers up to 5 days after baiting. Valley pocket gophers (n=744) were examined for the presence of blue dye in their cheek pouches, skin/fur, and fat. We expected that if gophers moved the bait, their cheek pouches and fur would be marked; if they consumed bait, their fat would be marked. In alfalfa, 54.2%, 46.8%, and 65.7%, of gophers were marked (trapping on days 5–9) by blue dye in one or more of their cheek pouches, skin, fur, or subcutaneous fat in the winter, summer, or fall, respectively. In orchards, 57.1% of gophers were marked in winter and 53.4% in summer. Of those that were marked, all (100%) had their fat dyed blue, followed by skin/fur (34.4% males: 43.7% females) and cheek pouches (5.7% males: 10.1% females). ANOVA results indicated no difference in seasonal marking efficacy in either alfalfa or orchards (F=3.59, P=0.0598 and F=0.12, P=0.7384, respectively). The usefulness of 1.6% Dupont oil blue A dye as a marking agent for Valley pocket gophers was not demonstrated overall or for any season in either habitat. Therefore, a better marker for this gopher is needed. Some factors that may have influenced these results were discussed including: (1) baiting methodology ( 66% of the bait sites were devoid of bait at the end of the study), (2) species specific dye properties, (3) bait acceptance (i.e. aversion to the dye), or (4) availability of alternative foods

Efficacy of a two-ingredient fumigant on Richardson's ground squirrel

In July 1981, efficacy data were obtained on a new two-ingredient gas cartridge by field testing against Richardson's ground squirrels (Spermophilus richardsonii) in a sagebrush-rangeland pasture. The gas cartridge contained 97 g of a sodium nitrate (65%) and charcoal (35%) mixture and upon ignition generated mainly carbon monoxide with a small quantity of carbon dioxide. We live-trapped 53 (24 male and 29 female) ground squirrels, equipped each with a 164 MHz radio transmitter, and then released each at the point of capture. Later we located each ground squirrel and treated its main burrow and all burrows within 3 m by inserting ignited gas cartridges. After treatment the location of each radio-equipped ground squirrel was plotted. Ground squirrels showing no movement were presumed dead; death was confirmed by burrow excavation. Success rate was 84% as 41 of 50 (18 males and 23 females) died (82%) and 8 survived (16%). The radio transmitter on 1 (2%) failed immediately after treatment. Efficacy was estimated at 83.7%, which exceeds the 70% minimum standard established by the EPA. Thirty-eight ground squirrels died in burrows at depths ranging from 7.6 to 132.1 cm (mean = 74.7 ± SE 5.2 cm), and 3 died in nests at depths ranging from 94.0 to 182.9 cm (mean = 133.0 ±SE 26.2 cm). Seven of the eight survivors were retrapped. Factors contributing to survival are discussed, including soil porosity and moisture content, as well as squirrel body weight. Recommendations for further testing are presented