Abstract: A petri dish residue-potter tower method was used to determine the concentration which discriminate between the susceptible and propargite-resistant strains of Tetranychus urticae. A concentration 0.04% ai (active ingredient) of propargite was selected as the discriminating concentration. This discriminating concentration could be used in propargite resistance detection and subsequent monitoring. The estimate of dominance for F1 hybrid females was -0.08 and -0.07 for R X S and S X R , respectively. These values indicate that propargite resistance in T. urticae has no substantial dominance. The response of the reciprocal F1 cross hybrids to propargite was, therefore, intermediate and no effort was made to select a concentration for discrimination between the hybrids and either of the strains.