RESUMEN
The Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), is an important pest in the western Great Plains of the United States, where it causes hundreds of millions of dollars of losses to barley and wheat production through reduced yields. Experiments to evaluate the effect of early planting and resistance in barley (Hordeum vulgare L.) on D. noxia were conducted at Fort Collins, CO; Tribune, KS; and Sidney, NE, in 2007, 2008, and 2009. Treatments included two planting dates and four cultivars, the D. noxia-resistant barley cultivars 'Stoneham' (Otis*4/STARS 9577B) and 'Sidney' (Otis*4/STARS 9301B), the susceptible cultivar 'Otis', and Otis treated with thiamethoxam. In tiller samples collected from May through early July, consistently lower D. noxia populations were found in plots planted â30 d earlier than normal at Fort Collins in all three years, and at Tribune in 2007. With one location-year exception, lower D. noxia populations occurred on plants of resistant varieties or the susceptible variety Otis treated with thiamethoxam than on untreated Otis plants. There were no significant differences in D. noxia populations produced on plants of either resistant variety and susceptible Otis plants treated with thiamethoxam. Interactions between resistant varieties and early planting resulted in reduced D. noxia populations at Fort Collins in 2007 and 2009, and at Tribune and Sidney in 2007. Planting D. noxia-resistant barley varieties, planting varieties earlier than normal, and the synergistic effect of resistant variety and early planting can significantly reduce D. noxia infestations on barley in the western High Plains.