Insecticide residues in wool from sheep jetted by hand and via automatic jetting races

Abstract

Summary. Sheep with 8 months wool were jetted according to registered label instructions with diazinon or cyromazine using a standard Harrington automatic jetting race, a modified jetting race or by hand. The modified jetting race delivered more insecticide solution than the standard machine or hand jetting. Sequential insecticide residue analysis of the wool that had been directly treated was used to calculate the half-lives of diazinon and cyromazine when applied by the 3 techniques. The half-life of diazinon applied by hand jetting was about 27 days. The half-life of hand-jetted cyromazine was about 75 days on sheep. Insecticide half life was much lower on sheep treated via the standard Harrington automatic jetting race. This is believed to be because, unlike hand jetting which gives good liquid penetration of the fleece, much of the applied chemical remains on the outside of the fleece where it is subject to greater environmental breakdown. Diazinon residues measured in bale core samples were significantly higher in wool from hand-jetted sheep compared with sheep treated via the modified automatic jetting race which in turn were significantly higher than those from sheep treated via the standard Harrington automatic jetting race. Cyromazine residues measured in bale core samples were not significantly different for sheep that had been hand-jetted or jetted via the modified automatic jetting race. However, residues found in bale samples of wool taken from sheep treated via the standard Harrington automatic jetting race were significantly lower. This is thought to be due to the efficiency of application and the slower degradation of cyromazine in wool.