Behavior of amitraz in cattle dipping baths

The settling rates of 0.025% w/v amitraz (used as a 50% w/w active ingredient wettable powder) and lime stabiliser (0.7% Ca(OH)2) were studied in cattle dipping baths in the Tick Quarantine Area of northern New South Wales. Although lime settled more rapidly than amitraz, the rate for both decreased as the number of cattle dipped increased. After a total of 1,200 head had been dipped the settling rate during the hour following stirring was negligible, and re-stirring was not necessary within the hour following use. Baths could also be cleaned of heavy sediment by scooping without significant loss of chemicals. When the bath volume was allowed to decrease to 2,100 liters below working volume no significant changes in amitraz and Ca(OH)2 concentrations occurred. Data collected from 796 baths showed a significant concentration change of +0.00066% amitraz and -0.017% Ca (OH)2 per 1,000 head of cattle. Replenishment per 700 liters of water with 254 g amitraz was found to be in good agreement with 250 g recommended by the manufacturer, while 12.53 kg for lime was substantially more than the 10 kg recommended.