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 single application of the 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 100 ppm (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 100 ppm (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 wasa smallprairie dog town on a private ranch located in a sagebrush/grassland

pasture. The site wassparselyvegetated with forbs and cactus. The studywas conducted during late September, 1990.

METHODS

A prairie dog town located within the studyarea was divided into three plots. One

plot served as a no treatment control to monitor prairie dog activity. The second

plot received one application of 100ppm chlorophacinone on whole, hulled oats.

The third plot received twoapplicationsofthe chlorophacinone bait 48 hours apart.

The bait was applied using a calibrated dipper to scattering one tablespoon (9g) of

bait near each burrow entrance.

Efficacywas determined by observingand countingactiveprairie dogs before and

after treatment. Visual countsusingbinocularswere obtained on marked counting

areas within treated and control plots. Three countswere made at fiveminute intervals each day on each plot for three consecutivesdaysimmediatelyprior to application and 7 and 14daysafter application. The nine pretreatment and posttreatment

visual countswere averaged to compute activityindices(AI) for each plot. Percent

reduction in activitycaused by 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 smallsample size and with no replica- ,it

tions. Therefore, more field testing is needed before valid conclusions can be made

concerning the efficacyof the test bait. Preliminary data does suggest that two applications of 100ppm chlorophacinone oat bait maybe effectivefor prairie dog control. Any future registration of chorophacinone for use on prairie dogswill depend

on concernsfor effects on nontarget species,particularlythe black-footed ferret.

ACKNOWLEDGMENTS

Thanks to Oregon Rodent Control Outfitters who supplied the bait used in this

studyand Lee Richardson for allowingthe use of his property.

LITERATuRE CITED

Sullivan,D. and M. Sullins. 1990. Field evaluation of chlorophacinone treated bait

for management of ground squirrelsin Montana. Montana Department of Agriculture. Helena, Montana. TechnicalReport 90-03. 6pp.

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