In horticulture, there are increasing reports of reduced effects of insecticides and acaricides without any doubtful proof. The essential factor is knowledge about the amount of active ingredient that actually deposited on the treated surfaces during the preparation of various resistance tests in the laboratory (bioassays). Using the example of pesticide applications in rose crops, we show that the analysis of active ingredient deposits in horticultural practice is also an essential component for assessing the sensitivity of the pests. We document here the origin of the leaves used for the bioassays and describe in detail the application of the pesticides to the leaf discs using the Potter tower. The individual analysis results of the active ingredient quantities that were applied to the leaf discs in the laboratory and to the insides of the roller rim glasses in the laboratory and that remained attached to rose leaves in horticultural practice are attached.