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 popula tions and barley yellow dwarf virus (BYDV) incidence in barley was st udied in Mall Nʹarok. Kenya. RllOpll/osipllIllfl pml; (L.) and A4elOp%phiul1I dirhodutl1 (WLK.) were common ap hid species, but other cereal a phids present were RliopaioSli!illlm maidis (Fitch), S!iobiol1 aren(le (F.), S(ʹhi~aphis gramil1ul11 (Rond.) and HysferollC!ura sefaria Thom. The incidence of BYDV was significantly decreased in plots sown with seed that had been treated wilh imidacloprid (NTN-33893. Gaucho) and subsequently sprayed wilh 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 I OOO-grain weight were not significa ntly differcl1l among insecticide treatments in the early-planted crop . In the late-planted crop. the yield increase with seed trea lment alone was highly significant (P < 0.00 1). with a yield increase of 36--43 % , morc than that of the untrea ted control. Grain yield was significa nlly (P < 0.05) negatively correlated with the lotal number of ce real aphids, as well as with the numbers of R. padi alone