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Rodents cause extensive damage to sugarcane (Saccharum spp. hybrids) in southern Florida (Samol 1972). Losses have been estimated as high as $235/ha (Lefebvre et al. 1978). Cotton rats (Sigmodon hispidus) and roof rats (Rattus rattus) are responsible for most of the damage (Holler et al. 1981). In-field treatment is required for effective reduction of rat populations because of the distribution and restricted movement patterns of rats within fields (Lefebvre et al. 1985a). Zinc phosphide (2%) baits are the only rodenticide baits registered for in-field use in Florida sugarcane. A preliminary test of in-crop aerial application of ZP Rodent Bait AG3 (Bell Laboratories, Inc., Madison, Wis.) in Florida showed poor results in reducing roof rat populations; only 7 of 40 (18%) radio-collared rats in 2 treated fields died whereas none of 38 radio-collared rats in 2 control fields died (Lefebvre et al. 1985b). Furthermore, no significant difference in pre- and post-treatment trapping success between treatment and control fields was observed. Donovan (1986) reported that numbers of cotton rats trapped in fields treated with this bait differed from those trapped in untreated fields; however, degree of efficacy was not discussed. Our study was conducted to obtain preliminary data on the effectiveness of ZP Rodent Bait AG in reducing cotton rat populations in Florida sugarcane. The study also provided information on the rate of disappearance of the bait following application.