Influence of Grazing on Russian Wheat Aphid (Homoptera: Aphididae) Infestations in Winter Wheat

Abstract

<i>The impact of grazing on infestations of Russian wheat aphid</i>, Diuraphis noxia <i>(Mordvilko), has not been well documented. This study was conducted to determine whether grazing Russian wheat aphid infested winter wheat can reduce subsequent infestations and consequently protect yields. Three cultivars of hard red winter wheat were grazed in the spring before plants reached the jointing growth stage (Zadoks 30). Russian wheat aphid infestations were evaluated 1 and 5 wk after removal of cattle. There was a short-lived but significant reduction in infestation levels of Russian wheat aphid in grazed wheat compared with ungrazed wheat. One week after removal of cattle, infestation levels in all varieties were reduced by 75% in the grazed wheat compared with ungrazed wheat. At early stem elongation (Zadoks 31) growth stage, the infestation in the un g razed wheat was approaching the currently accepted economic threshold levels for Russian wheat aphid while densities in the grazed stand would not have justified an insecticide application. Five weeks after removal of cattle, the reduction in Russian wheat aphid infestation in grazed wheat was no longer evident. Greenbug</i>, Schizaphis graminum <i>(Rondani), was not detected before grazing but was found during subsequent evaluations. Grazing had no effect on greenbug infestations because they occurred during or after grazing was completed. Grazed wheat had significantly higher yields but significantly lower test weights than ungrazed wheat. Spring grazing can be a useful component in the overall management of Russian wheat aphid in southeastern Colorado.</i>