Efficacy of Zinc Phosphide Broadcast Baiting for Controlling Richardson's Ground Squirrels on Rangeland

Abstract

Zinc phosphide, a potential replacement rodenticide for strychnine or 1080, was field tested on 3 populations of Richardson's ground squirrel. Populations were estimated pretreatment and posttreatment by mark-recapture sampling techniques. We broadcasted a 2% zinc phosphide grain bait at 5.1 kg per swath ha. Swath widths measured 6.1 m, 16.0 m of untreated areas remaining between swaths. Treated populations decreased an average of 85.1 +/- SE 6.4%. Differences in pretreatment and posttreatment population decline between treated and control populations were significant (P = 0.096). No mortality was detected among nontarget animals. The 85.1% efficacy achieved by broadcast baiting exceeded the minimum standard of 70.0% established by the Environmental Protection Agency for the registration of a rodenticide. Registration, however, will require nontarget hazard testing and further efficacy testing in other geographical locations.