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, insecti cides were applied to control aphids and thereby diminish the spread o f aphid-transmitted barley yellow dwarf luteovirus (BYDV). Disease pro gress was followed over time by enzyme-linked immunosorbent assay (ELI SA) on leaf samples using antiserum specific to BYDV serotype PAV. Two foliar applications of either of two newer generation synthetic pyret hroid insecticides, alpha-cypermethrin or beta-cyfluthrin, sprayed bef ore flag leaf emergence and at rates as low as 12.5 g a.i./ha, decreas ed 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 4 5% and increased grain yield by up to 14%. Seed treatment with imidacl oprid (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 foll owed by two foliar sprays of alpha-cypermethrin, BYDV incidence was de creased 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 pyr ethroids markedly decreased the numbers of aphids. Numbers colonizing plants were mostly lower than 10 per tiller on nontreated plots, sugge sting the grain yield increases resulting from insecticide application were due to control of BYDV rather than to decreased aphid feeding da mage. To minimize BYDV-induced grain yield losses in autumn-sown cerea ls, protection by insecticides should be provided from soon after plan t emergence until the twelfth week of plant growth.