Modelling pesticide residues on greasy wool: surveys of the insect growth regulators triflumuron and diflubenzuron

Abstract

Surveys have examined the relationship between louse and flystrike treatments on farms and the resulting residues of insect growth regulators on greasy wool. These results have been summarised using a model of the on-farm survey data. The model estimated the amount of chemical taken up by the wool at application. This was based on experimental breakdown rates of these insecticides on wool determined in controlled trials. The data indicated that the backliner, triflumuron, when used off-shears within 24 h of shearing, was normally applied at slightly higher than the recommended rate on-farm and left an average residue of 30 mg/kg greasy wool at the following shearing 12 months later. Diflubenzuron, applied by dipping or jetting, was usually applied at lower than the recommended rates, and left an average residue of 40 mg/kg on the wool at shearing 12 months later. When treatment was applied to very short wool (<3 weeks after shearing) the residue was only about 20 mg/kg, but when applied at later times after shearing the residue at the following shearing was not closely related to the time of treatment. The model can be used to estimate the expected residue level and likely range of results from most standard insect growth regulator treatments. This will improve advice to producers so most can meet specified industry standards.