The control of barley yellow dwarf virus (BYDV) and its aphid vectors in minimum tillage (MT) and conventionally tilled (CT) winter barley by insecticide seed and foliar spray treatments was investigated in 2001, 2002 and 2003. Similar investigations were undertaken on winter wheat in 2004, 2005 and 2006. Aphids numbers in autumn and BYDV in spring on barley and wheat were significantly lower on MT relative to CT crops, in two of the six seasons. An insecticide spray at Zadoks growth stage (GS) 25 significantly reduced aphids and virus in both MT and CT crops in three of the six seasons of the study. An additional spray at GS 22 provided no benefit. Aphids were significantly fewer in three of the six seasons on crops grown from insecticide treated seeds, relative to untreated seeds. Both MT and CT barley sprayed at GS 25 had significantly fewer aphids than the seed treatment in one of the three seasons. Seed-treated MT and CT barley had significantly less BYDV than controls but significantly more than crops sprayed at GS 25. CT wheat grown from insecticide-treated seed had significantly less BYDV than controls. Overall, CT barley grown from insecticide-treated seed had 6-fold more BYDV than the sprayed crop, while untreated barley had 22-fold more than the spray treatment. In MT barley, the comparable values were 3- and 10-fold respectively. BYDV was almost exclusively the MAV strain. The grain yield for insecticide-sprayed CT barley was significantly greater in two of three seasons than that for untreated plots. In general, MT and CT barley receiving an insecticide spray had greater grain yield than barley grown from insecticide-treated seed, with differences being significant in one of three seasons. It is concluded that BYDV in MT and CT cereals is better controlled by applying a pyrethroid insecticide spray between GS 23 and 25, in autumn, than by treating the seed with a nitroguanidine-type insecticide. In MT crops, a single spray between GS 23 and 25 will give effective control of MAV-type BYDV.
