Ebb-and-flow systems can be used to apply systemic pesticides to greenhouse crops without worker exposure or runoff. However, there is little information on the efficacy of pesticides applied with ebb-and-flow systems. We are using silverleaf whitefly (Bemisia argentifolii) control on poinsettia (Euphorbia pulcherrima) with imidacloprid as a model system to study pesticide efficacy in ebb-and-flow systems. The objective of this study was to determine the effect of the amount of insecticide taken up by the pot on the efficacy of whitefly control. Different amounts of imidacloprid uptake were obtained by not watering the plants for 0, 1, 2, or 4 days before the imidacloprid application. The imidacloprid (132 g·L–1) was applied once when the roots of the cuttings had reached the side of the pots. These treatments were compared to an untreated control on ebb-and-flow and a standard drench application (100 mL) to hand-watered plants. Pots in the different subirrigation treatments absorbed 12 to 175 mL of imidacloprid solution. Four days after the application, leaf tissue of the hand-watered plants contained 8 to 20 times more imidacloprid than the subirrigated plants. Efficacy was determined from the percentage of surviving mature whiteflies after 2 days on the plants and by counting the number of immatures after 2 weeks. Surprisingly, imidacloprid efficacy was better in the subirrigated imidacloprid treatments than in the hand-watered treatment. Whitefly control in all subirrigated imidacloprid treatments was excellent, irrespective of the amount of imidacloprid solution taken up by the pots.