Development of Autumn Populations of Cereal Aphids., Rhopalosiphum padi (L.) and Schizaphis graminum (Rondani) (Homoptera: Aphididae) and Their Effects on Winter Wheat in Washington State

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Abstract
Planting winter wheat in early September is a common practice in much of eastern Washington. A number of agronomic benefits are associated with planting early, but there is also a higher risk of cereal aphids infesting the crop with early planting. Caged experiments were conducted in the field during two crop seasons (1979–1980, 1981–1982) to assess population development and direct feeding effects of two cereal aphids, Rhopalosiphum padi (L.) and Schizaphis graminum (Rondani), on winter wheat planted in early September and infested during the two-leaf, four-leaf, and two-tiller stages of development. Aphids were introduced at a rate of two to four per plant per species and allowed to feed uninterrupted until cold weather ended their activity in November. Data taken were: plant height, heads per plant, root and foliage weights, test weight, and grain yield. R. padi, singly or in combination with S. graminum, was generally more prolific than S. graminum. The largest aphid populations encountered were on wheats infested initially at the two-leaf stage. Injury to wheat was highest where aphid infestations started at the two-leaf stage, intermediate to none at the four-leaf stage, and none at the two-tiller stage. Mixed populations on two-leaf wheats caused the greatest damage, followed by pure populations of R. padi. S. graminum generally caused the least damage.