Montana Department of Agricutture Environmental Management Division Technical Services Bureau

Helena, Montana 59620

USE OF CHLOROPHACINONE TREATED BAIT FOR MANAGEMENT OF BLACK-TAILED PRAIRIE DOGS IN MONTANA By Monty Sullins Vertebrate Pest Specialist

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ABSTRACf A range findingfield trial was conducted to determine the efficacyof a 100ppm chlorophacinone oat bait for controllingblack-tailedprairie dogs. A singleapplication ofthe bait reduced prairie dog numbers 72% and two applications 48 hours apart resulted in a 96% reduction in activity.INTRODUCTION Currently, zinc phosphide is the only rodenticide registered for use on prairie dogs that is practical for large acreage applications. Applicators often complain of variable and less than satisfactory results when using it. Aluminum phosphide burrow fumigants are also registered but require moist soil conditions, are labor intensive, and are practical for only small area applications. Sullivan and Sullins (1990) reported good results using 100ppm (0.01 %) chlorophacinone bait for reducing numbers of Richardson (Spennophilus richardsonii) and Columbian (S. columbianus) ground squirrels. Data is not currently available concerning the efficacy of this bait on other field rodent species in Montana. This report evaluates it as an alternative means for controlling black-tailed prairie dogs (Cynomys ludovicianus). OBJECTIVE
The objective of the field study was to conduct a range finding study to determine if<9 a 100ppm (0.01 %) chlorophacinone bait would have potential as a black-tailed prairie dog toxicant. STUDYAREA The studywas conducted in Carbon Countynear Fromberg, Montana. The study site was a smallprairie dog town on a private ranch located in a sagebrush/grassland pasture. The site was sparselyvegetated with forbs and cactus. The studywas conducted during late September, 1990. METHODS A prairie dog townlocated withinthe study area was dividedinto three plots. One plot served as a no treatment control to monitor prairie dog activity. The second plot received one applicationof 100ppm chlorophacinone on whole, hulled oats. The third plot received two applications ofthe chlorophacinonebait 48 hours apart. The bait was appliedusing a calibrated dipper to scattering one tablespoon (9g) of bait near each burrow entrance. Efficacywas determined by observingand counting activeprairie dogs before and after treatment. Visual countsusingbinocularswere obtained on marked counting areas within treated and control plots. Three counts were made at fiveminute intervals each day on each plot for three consecutivesdaysimmediatelyprior to application and 7 and 14daysafter application. The nine pretreatment and posttreatment visualcounts were averaged to compute activityindices (AI) for each plot. Percent reduction in activitycausedby the bait was computed by the formula:Pretreatment AI

- Posttreatment AI Percent reduction = ----------------------------------------------- In Activity Pretreatment AI X 100

Treated plots were observed for prairie dog carcassesand nontarget mortalities. RESULTS Prairie dog numbers were reduced 72% and 96%, respectively, on the single and double bait application plots. No significant change in activity occurred on the control plot and no prairie dog carcasses or nontarget mortalities were observed. DISCUSSION The data in this trial were obtained using a small sample size and with no replica- ,it tions. Therefore, more field testing is needed before valid conclusionscanbe made concerningthe efficacyofthe test bait. Preliminary data does suggest that two applications of 100ppm chlorophacinone oat bait maybe effectivefor prairie dog control. Any future registration ofchorophacinone for use on prairie dogswill depend on concerns for effects on nontarget species,particularlythe black-footed ferret. ACKNOWLEDGMENTS Thanks to Oregon Rodent Control Outfitters who supplied the bait used in this study and Lee Richardson for allowingthe use ofhis property. LITERATuRE CITED Sullivan,D. and M. Sullins. 1990. Field evaluation ofchlorophacinone treated bait for management ofground squirrels in Montana. Montana Department ofAgriculture. Helena, Montana. Technical Report 90-03. 6pp.

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