Effect of fall infestations of Russian wheat aphid (Homoptera: Aphididae) on winter wheat yield and quality on the Canadian prairies

The effect of fall infestations of Russian wheat aphid, Diuraphis noxia (Mordvilko), was investigated in winter wheat in southern Alberta, Canada. In 3 trials, yield losses ranging from 25 to 37% were prevented by insecticide treatment of the Russian wheat aphid. The highest yield loss was associated with aphid densities of 4.81 +/- 0.61 aphids per plant in the early seedling stage (Zadoks I3) on 11 September 1990; subsequently, aphid densities in the control plots increased to 90.68 +/- 7.68 per plant by the last sampling date on 19 November. In all 3 trials, aphids did not survive the winter, but the fall infestations resulted in stand reductions through winterkill ranging from 28 to 35%. On a per plant basis, those plants that survived the winter fully recovered from aphid damage during the growing season. Quality analyses indicated that the overall effects on breadmaking quality were minor. There were no significant relationships between aphid densities and yield. However, yield was significantly correlated with plant stand in the spring, which in turn was significantly correlated with aphid densities during the previous fall. These data support the conclusion that, in southern Alberta, Russian wheat aphid damage is expressed in stand reductions through winterkill and that yield reductions occur primarily when stand reductions become significant. Once they survive winter, previously infested plants recover from aphid damage and yield losses are minimal, provided plants are not reinfested in the spring.