As a powder seed treatment on wheat, barley and oats a mixture of quinacetal-sulphate + maneb + γ -BHC gives a disease control spectrum similar to that of organo-mercury standards, except against oat leaf spot (Pyrenophora avenae) on which quinacetal-sulphate + maneb is more effective. In small-plot trials under poor seed-bed conditions the quinacetal-sulphate mixture gave improved crop establishment compared with organo-mercury standards possibly due to improved activity against soil-borne pathogens. Overdose rates were better tolerated than overdoses of organo-mercury + γ -BHC. Of 63 farmers in the UK supplied with seed treated in commercial equipment, 60 obtained improved plant stands with quinacetal-sulphate + maneb + γ -BHC in comparison with organo-mercury standards. The farm results were achieved in favourable as well as unfavourable seed-bed conditions and appear to be due to the better tolerance by individual cereal seeds of overdoses of the quinacetal-sulphate mixture.