The use of acaricides of high toxicity in the production and handling of ornamental plants should be a matter of consumer concern. The susceptibility of two populations of Tetranychus urticae was assessed: one collected from Primula obconica Hance and the other from Convolvulus arvenis L. as susceptible reference strain to the acaricides dicofol, abamectin alone and mixed with the surfactant phosphatidylcholine, azadirachtin, sulfur, pyridaben and fenazaquin. The evaluated parameters were mortality, lethal concentration 50% (LC50) and 90% (LC90), lethal time 50% (LT50) and 90% (LT90), effectiveness and index of resistance (IR). The experimental design was completely at random. Each treatment had 1/4, 1/2, 1, 2 and 4X of the doses indicated by the manufacturer, five replicates and were sprayed with a Potter spray tower. The results showed that the LC50 for azadirachtin and sulfur was significantly high. Regarding the population from P. obconica, abamectin alone and in mixture with phosphatidylcholine and fenazaquin showed the highest efficiency. Azadirachtin and sulfur were the acaricides showing the slowest activity and the resistance index indicated that the population collected in P. obconica should be considered susceptible to all the evaluated acaricides.