Tillage advice: Recent rain was critical for crops
Last weekend's rain brought much needed moisture to spring crops. Emergence is uneven with drier areas in fields having poor ground cover and moisture retentive areas reasonably well covered in.
Areas with poor cover are a prime target for migrating aphids, which may or may not be carrying barley yellow dwarf virus.
Teagasc trials have shown yield reductions in late April sown crops of 1.1t/ha (20pc) where BYDV infection was high and 0.36t/ha (7pc) where BYDV levels were low. Best control is achieved with a single insecticide at the four-leaf stage (gs 14).
In recent years we have found resistance by aphids to pyrethoids. Currently there is no alternative insecticide so if you fail to control aphids with one insecticide on barley or oats there is no merit in going back in with a different product.
In fact doing so will increase the damage as the pyrethoids kill natural predators. This year aphid numbers are higher than normal. Aphids migrate in May when temperatures are over 15C and when there is little wind or rain present.
In coastal areas and areas with a history of high BYDV infection it is difficult to ignore the standard advice of applying an aphicide at the four-leaf stage.
However in other parts of the country strong consideration should be given to not using an aphicide and to leave natural predators do their work particularly if you get rain to coincide with the four leaf stage of the crop.
Heavy rain will drown aphids as they are washed into pore spaces in the soil which fill with rainwater. If you fail to get rain in that period or have patchy crops you may then resort to your insecticide.