Economic Injury Levels for the Russian Wheat Aphid (Homoptera: Aphididae) on Winter Wheat in Several Climate Zones

Abstract

Research was conducted in 4 states (Colorado, Montana, Texas, and Washington) to determine the economic injury level for the Russian wheat aphid, Diuraphis noxia (Kurdjumov), as affected by climate zone and wheat growth stage. Fall infestations were established on winter wheat at the 2-leaf and 2-tiller growth stages. Russian wheat aphid infestations did not develop well on the 2-tiller stage wheat because late fall temperatures became too cold before the infestation period was complete. In the coldest climate zones, where winter kill of wheat becomes a factor, the loss value for 2-leaf wheat will be 1% per percentage infested or damaged tillers and 1.1% per infestation or damage day. This was 3 times greater than the loss in the southern climate of Texas and 1.6 times greater than the loss in the Pacific Northwest (Washington). Therefore, different fall infestation economic injury levels will be used in different climate zones in the United States. Russian wheat aphid infestations on winter wheat were initiated in the spring at spring regrowth, one node, and boot growth stages. Losses from Russian wheat aphid infestations in Colorado in the spring were similar to those reported in earlier research in Texas, 0.5% loss in bulk seed weight per percentage of infested or damaged tillers.