Effects of sowing date and insecticides on cereal aphid populations and barley yellow dwarf virus on barley in Kenya

The effects of the date of sowing and insecticide sprays on aphid populations and barley yellow dwarf virus (BYDV) incidence in barley was studied in Mau Narok, Kenya. Rhopalosiphum padi (L.) and Metopolophium dirhodum (WLK.) were common aphid species, but other cereal aphids present were Rhopalosiphum maidis (Fitch), Stiobion avenae (F.), Schizaphis grammum (Rond.) and Hysteroneura setaria Thom. The incidence of BYDV was significantly decreased in plots sown with seed that had been treated with imidacloprid (NTN‐33893, Gaucho) and subsequently sprayed with foliar insecticide (Cypermethrin). Yield loss due to BYDV was also significantly different between the treatments and between the earlyplanted and the late‐planted crop (P < 0.05). Grain yield and 1000‐grain weight were not significantly different among insecticide treatments in the early‐planted crop. In the late‐planted crop, the yield increase with seed treatment alone was highly significant (P < 0.001), with a yield increase of 36‐43%, more than that of the untreated control. Grain yield was significantly (P < 0.05) negatively correlated with the total number of cereal aphids. as well as with the numbers of R. padi alone.