Comparisons of Strychnine and Zinc Phosphide in Prairie Dog Control

Efficacy and safety are primary considerations in registration and use of toxicants for vertebrate pest controlo Strychnine (0,5$) and zinc phosphide (2$) are currently registered by EPA for prairie dog control, but continued registration is uncertain. Two percent zinc phosphide bait has been suspected of producing lower and more erratic results than strychnine baito In our study in western Nebraska in fall 198MD indices based on changes in burrow activity showed no difference in efficacy (£=0,66) or variability (£=0<,7) of control for strychnine and zinc phosphide, however neither toxicant consistently gave effective control of blackballed prairie dogso Costs for proper control (prebait and poison) were similar for strychnine and zinc phosphide,, For clean=up of surviving prairie dogs, fumigation with aluminum phosphide was more effective than shooting and more cost effective than shooting combined with fumigation,, Observed nontarget wildlife losses (M horned larks and 2 lagomorphs) were small and of doubtful biological significance. Availability of both strychnine and zinc phosphide is part of the flexibility needed in an integrated approach to prairie dog controlo Also, there is need for additional toxicants or methods that will give more consistently efficacious control. °University of Nebraska Panhandle Research and Extension Center, Scottsbluff, Nebraska 693615 current address; Georgia Dept, of Natural Resources, 2150 Dawsonville Hwy,0 Gainesville, GA 30501, Department of Forestry0 Fisheries and Wildlife, University of Webraska0 Lincoln, Nebraska 68583=0819,, INTRODUCTION The blackballed prairie dog (£3momy_3_ ludovicianua) is an abundant rangeland pest of increasing concern to farmers and ranchers in the Great Plains,, In western Nebraska, prairie dog populations increased approximately 60? between 1970 and 1980 (Nebraska Game & Parks, unpubl, data). Although little data are available since 1980, landowner complaints suggest that an upward trend has continued to the present. Notable increases also have been observed in other areas of the Great Plains (Fagerstone 1981), Prairie dogs and associated grazing wildlife have been reported to reduce total forage availability to livestock by 2k to 37? on established prairie dog towns (Hansen and Gold 19770 O'Meilia 1980, Hyde 1981), However, prairie dogs increase the perennial grasses that are heavily utilized by livestock (Bonham and Lerwick 1976, Gold 1976, Coppock 1980), Since the effects vary among geographical areas and plant communities (Fagerstone 1981), there is no consensus on the amount of rangeland damage that is caused. In most situations economic loss is likely and long term rangeland damage is possible when substantial livestock grazing occurs on active prairie dog towns. Poison grain bait is the most practical and cost effective technique for controlling prairie dogs (Boddicker 1983)o Strychnine and zinc phosphide are the only toxicants currently federally registered for this purpose, although Compound 1080 was widely used in the past and is still used in Colorado for prairie dog control. In 1980 the U0So Environaental Protection Agency (EPA) proposed cancellation of strychnine for prairie dog control (EPA 1980a, 1980b)o The Scientific Advisory Panel reviewing EPAs recommendations on strychnine withheld support for cancellation in part because of