Use of imidacloprid and newer generation synthetic pyrethroids to control the spread of barley yellow dwarf luteovirus in cereals

In seven field experiments with wheat and oats sown in autumn, insecticides were applied to control aphids and thereby diminish the spread of aphid-transmitted barley yellow dwarf luteovirus (BYDV). Disease progress was followed over time by enzyme-linked immunosorbent assay (ELISA) on leaf samples using antiserum specific to BYDV serotype PAV. Two foliar applications of either of two newer generation synthetic pyrethroid insecticides, alpha-cypermethrin or beta-cyfluthrin, sprayed before flag leaf emergence and at rates as low as 12.5 g a.i./ha, decreased spread of BYDV by up to 75% and increased grain yields by up to 41%. These pyrethroids were more effective in decreasing BYDV spread than foliar applications of pirimicarb (150 g a.i./ha) or dimethoate (320 g a.i./ha), two applications of which decreased BYDV spread by up to 45% and increased grain yield by up to 14%. Seed treatment with imidacloprid (70 g a.i./ha) delayed BYDV spread in wheat and oats for up to 6 weeks after plant emergence. When imidacloprid seed dressing was followed by two foliar sprays of alpha-cypermethrin, BYDV incidence was decreased by up to 88%, and grain yield was increased by up to 76%. The predominant colonizing aphid species was Rhopalosiphum padi. Dressing seed with imidacloprid and/or foliar applications of the synthetic pyrethroids markedly decreased the numbers of aphids. Numbers colonizing plants were mostly lower than 10 per tiller on nontreated plots, suggesting the grain yield increases resulting from insecticide application were due to control of BYDV rather than to decreased aphid feeding damage. To minimize BYDV-induced grain yield losses in autumn-sown cereals, protection by insecticides should be provided from soon after plant emergence until the twelfth week of plant growth.