Control of barley yellow dwarf was studied in six-row plots of two oat cultivars using three rates (0.6, 1.2, and 1.8 g a.i. kg -1 seed) of imidacloprid, a seed-treatment insecticide. All insecticide treatments decreased the percentage of infected plants. Yield increases of up to 112% were observed in treated plots of a moderately susceptible cultivar inoculated with viruliferous aphids carrying barley yellow dwarf virus BYDV-PAV-IL. Insecticide-treated plots of a tolerant cultivar inoculated with BYDV-PAV-IL yielded up to 23% more than nontreated plots. In a similar study with four soft red winter wheat cultivars, all insecticide treatments decreased the percentage of infected plants, with the highest dose providing the most protection against BYDV infection. Yields were increased up to 21% in treated plots of a susceptible cultivar inoculated with viruliferous aphids carrying BYDV-PAV-IL. Noninoculated insecticide-treated plots also yielded an average of 14% more than noninoculated nontreated plots.