Efficacy and degradation of fipronil applied to cotton for control of Anthonomus grandis grandis (Coleoptera: Curculionidae)

Fipronil was applied to cotton Ly ground sprayer at ultralow volume and conventional spray rates. Boil weevil mortality and residue analysis of fipronil and its metabolites at 0, 1, 2, 3, and 6 d after application were used to evaluate treatments. An evaluation of the toxicity of fipronil and metabolites to bell weevils also was conducted. The order of toxicity (LD50) of fipronil metabolites at 48 h was sulfide > fipronil > sulfone > desulfinyl. Differences in percentage of mortality between treatments did not occur until 3 d after application when the ultralow volume application had higher mortality (98%) than the conventional (85%) spray rate. There were no differences in mortality between treatments at 6 d after application. Fipronil residues were present oil the leaf surface longer and in higher amounts when applied in cottonseed oil at 1.17 liter/ha than when applied in water as a conventional application at 97 liter/ha.