RESIDUES IN RUNOFF AND ON LEAVES OF AZINPHOSMETHYL AND ESFENVALERATE APPLIED TO SUGARCANE

A study of azinphosmethyl and esfenvalerate runoff losses after applic ation to sugarcane for control of the sugarcane borer was conducted on the St. Gabriel Research Station of the Louisiana State University Ag ricultural Center. In a 2nd study, leaf loads of these insecticides we re determined. The 24-h LC(50) (27.8 mu g/liter) of azinphosmethyl to bluegill was exceeded in 2 of the 9 runoff events that occurred during the study period but because of expected dilution effects downstream from the site of application, only the concentration (261 mu g/liter) that occurred in runoff 2 d after application was high enough to cause concern. The 24-h LC(50) (4,530 mu g/liter) of azinphosmethyl to chan nel catfish fingerlings was not exceeded. The day 2 level of esfenvale rate (1.91 mu g/liter) did not exceed sufficiently the 24-h LC(50) (0. 42 mu g/liter) of this insecticide with respect to bluegill to cause c oncern; the toxicity of the pyrethroid to channel catfish (2.35 mu g/l iter) was not surpassed. A reduced (two-thirds) rate application of es fenvalerate with acephate did not lead to concentrations of the pyreth roid in runoff higher than its toxicity to these fish species. The tim e to 50% disappearance (DT50) of azinphosmethyl leaf residues varied f rom 0.90 to 1.09 d, which was similar to the DT50 (0.76 d) of the chem ical in runoff. Esfenvalerate on leaves was longer lived (DT50 = 2.46- 4.46 d). These runoff and leaf residue data indicate that azinphosmeth yl or esfenvalerate applications to sugarcane should cause little conc ern for toxic effects on bluegill or channel catfish except possibly i n the event of runoff within 2-3 d of application of the azinphosmethy l (possible bluegill toxic effects) or within 1 d of esfenvalerate app lication (possible toxicity to both fishes). Reduced rate applications would be of substantially less concern.