Reduced agent-area treatments (RAAT) for management of rangeland grasshoppers : efficacy and economics under operational conditions

The Reduced Agent-Area Treatment (RAAT) approach involves applying low rates of insecticides in intermittent swaths to control grasshopper infestations in an effort to achieve a more economically and environmentally sound pest management strategy compared to traditional blanket applications at high rates. Operational-scale (>250 ha) insecticide tests on Wyoming rangeland grasshopper infestations (18-56 grasshoppers/m2 ) at two sites in 1997 revealed that carbaryl yielded 94% control as a blanket treatment (560 g/ha) and 81% control as a RAAT application (280 g/ha applied to 50% of the infested land). Malathion yielded 90% control as a blanket treatment (683 g/1 ha) and 91 % control as an RAAT application (342 g/ha applied to 80% of the infested land), and fipronil (4 g/ha) yielded 98% control as a blanket treatment and 92% control when applied to 33% of the infested land. One year after treatment, the RAAT and blanket-treated plots had 2-4% (Pollet Ranch) of the densities in untreated plots. Economic analysis showed that the greatest benefit:cost ratio was obtained with the fipronil_RAAT method, followed by carbaryl-RAAT, malathion-RAAT, ma-lathion-blanket, fipronil-blanket, carbaryl-blanket. The worst-case out-come of fipronil and carbaryl with a RAAT approach had a greater economic return than the best-case outcome of no treatment. Following blanket treatments, non-target arthropod abundance was highest in the fipronil plots, followed by carbaryl and malathion; arthropod biomass was higher in the carbaryl plots than fipronil and malathion. In RAAT plots, arthropods were generally less impacted than in the blanket plots, with the least reduction caused by fipronil and carbaryl. Thus, the RAAT tactic appears to be economically and environmentally superior to blanket treatments under large-scale, operational conditions. (Résumé d'auteur