Effect of Pesticide Treatments on Nontarget Organisms in California Rice Paddies: I. Impact of Triphenyltin hydroxide: II. Impact of Diflubenzuron and Triflumuron

An application of triphenyltin hydroxide at 1.16 kg (AI)/ha to rice fields for stem rot (Sclerotium oryzae Catt.) control resulted in a significant reduction of 57% of the invertebrate taxa and 67% fewer individuals based on two collecting methods that sampled the nekton, neuston, and benthon. Populations of herbivores, carnivores, and filter feeders were sharply reduced after treatment, and most remained so through the 28th day following application. By day 50 many of the winged species recovered in both numbers and diversity. However, recovery of benthic organisms was slower or not at all for most Crustacea. An initial reduction followed by a strong resurgence was noted for the mosquito Culex tarsalis Coq., which was probably due to the significant reduction of five predaceous species. Two benzoylphenyl ureas, diflubenzuron and triflumuron, were evaluated in California rice fields to determine their ecological impact on populations of nontarget organisms. Modified minnow traps, drag net, and kellen dredge sampling devices were used in the collecting. Nontarget populations were sampled continuously throughout much of the 1985 and 1986 rice growing season. Total collections of nontargets showed only two Cypris species of seed shrimp crustaceans were significantly (P<0.05) reduced over time due to either chemical. One predaceous water boatman, Corisella decolor, showed the opposite pattern in that populations were significantly (P<0.05) lower in the control. Significant differences were not observed in species diversity or between treatments when grand means for all species by sampling device were calculated. A total of 35 families and 58 taxa were collected from these two studies.