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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's 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's 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 non- target hazards were discussed.
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