Crops that are more established are likely to be less exposed to a Barley Yellow Dwarf Virus (BYDV) attack according to a Teagasc entomologist.
Where aphids are concerned, their numbers and activity levels are determined by ambient temperature levels and as the days get warmer, aphid reproduction rates increase exponentially.
Teagasc has divided this year’s spring barley crops into different categories, from a BYDV threat perspective.
It has highlighted that crops sown in February are well beyond the critical growth stage.
Teagasc entomologist Dr. Louise McNamara said:
“The longer the period of time before aphids get active, the lower the impact that the insects will have on crop yields.
“The plan is to get to growth stage 31 before the aphids have an opportunity to alight on a crop.
“As a consequence, crops sown in February or early March would be considered to be at lower risk. This is because aphids were not as active during those earlier growth stages.”
However, she also warned that barley crops sown out at the end of April or early May would be considered to be at much higher risk from BYDV attack.
“This is because it’s warmer and aphids are more active. As a consequence, the insects will have the opportunity to get into crops at an earlier stage of growth,” Dr. McNamara added.
According to Dr. McNamara, the most effective way to control BYDV is to apply a single insecticide spray at growth stage 14.
“During a very mild spring, it will not be possible to remove all aphids from a crop.
“The spray may only give control, for around seven days. This depends on the ultra violet light breaking down the chemistry,” she said.
“It will not be possible to get zero BYDV control when there is high pressure from aphids. So, it’s a case of getting the maximum amount of cover from the insecticide. Trials have confirmed that this will be achieved when the crop is at growth stage 14.”
Dr. McNamara indicated that most of the aphicide-related research undertaken in Ireland was carried out in March and early April-sown crops.
Therefore, there is a case for applying an insecticide more than once on May-planted barley.
“The issue here is that multiple applications of the same chemistry drives resistance within the aphid population,” she said.
The Teagasc entomologist is also encouraging growers to check their crops for the presence of pests generally including grain aphids.