With reports of sheep scab mites ( Psoroptes ovis ) developing resistance to macrocyclic lactone (ML) injections,1 effective control through plunge dipping in 60 per cent diazinon is, therefore, essential in eradicating ML resistant mites. In terms of plunge dipping, three critical dip wash concentrations are recognised: n Initial (IC) – 400 mg/l for the current diazinon formulations; n Minimum lethal (MLC) – the lowest concentration in dip wash that is lethal to P ovis ; and n Maintenance (MC) – the lowest concentration likely to be maintained under field conditions when …