Winter wheat was planted over three dates (hereafter early, middle, and late; generally from late August to late September) to determine the effect on abundance of insect pests, incidence of viral plant disease, and plant growth and yield. The study was conducted simultaneously at two sites in South Dakota over three consecutive cropping seasons for a total of six site-years. Cereal aphids (Homoptera: Aphididae) were abundant or moderately abundant in three site-years. Aphids were more abundant in early versus late plantings for those 3 site-years, and more abundant in middle versus late plantings in 2 of the 3 site-years. Rhopalosiphum padi (L.) (bird cherry-oat aphid) was the most abundant cereal aphid at the Brookings site, whereas Schizaphis graminum (Rondani) (greenbug) was the predominant aphid at Highmore. Cereal-aphid abundance was not correlated with yield at Brookings, but negatively correlated at Highmore. Autumnal abundance of cereal aphids was correlated with incidence of barley yellow dwarf. Incidence ranged from 24 to 81 percent among 1999 plantings, and was highest in early plantings and lowest in late plantings; incidence was less than 8 percent in other cropping seasons. BYD incidence was negatively correlated with yield.