Influence of aphid species and barley yellow dwarf virus on soft red winter wheat yield

Yield loss in soft red winter wheat, Triticum aestivum L., caused by aphid-transmitted barley yellow dwarf virus (family Luteoviridae, genus Luteovirus, BYDV) was measured over a 2-yr period in central Missouri. Rhopalosiphum padi (L.) was the most common and economically important species, accounting for > 90% of the total aphids. Schizaphis graminum (Rondani), Rhopalosiphum maidis (Fitch), and Sitobion avenae (F.) made up the remainder of the aphids. Aphid numbers peaked at wheat stem elongation in 2003 with 771 R. padi per meter-row. In the 2003-2004 growing season, aphid numbers averaged seven aphids per meter-row in the fall and peaked at 18 aphids per meter-row at jointing. Wheat grain yield was reduced 17 and 13% in 2003 and 2004, respectively. Thousand kernel weights were reduced 10 and 5% in the untreated plots compared with the treated control in 2003 and 2004, respectively. Padi avenae virus was the predominate strain, accounting for 81 and 84% of the symptomatic plots that tested positive for BYDV in 2003 and 2004. Our results indicate that economic thresholds for R. padi are 16 aphids per meter-row in the fall and 164 aphids per meter-row at jointing.