Assessing the BYDV risk and planning control

Early-sown crops of winter barley are at high risk when it comes to barley yellow dwarf virus (BYDV), along with crops planted along the coast.

Aphids like warm temperatures, so crops planted from mid-September and into early October are more likely to see high populations.

If treating crops, an aphicide should be applied at the two to three-leaf stage.

However, before applying an aphicide growers should assess crops and previous performance. For example, growers should assess aphid numbers and if possible get an idea of the percentage of grain aphids present.

Field history then needs to be looked at. Was there a green bridge present up to sowing time which could have been hosting aphids? Is there known resistance to pyrethroids on your farm?

If your crop was planted early or you’re near the coast, it is at high risk and an insecticide will be needed. This may be a pyrethroid, or where you have known resistance growers in the high-risk category may look at using Teppeki.

Teppeki was cleared for use on winter barley this season, but is on the expensive side. Growers may find it practical in a high-risk situation.

If you are using a pyrethroid it will need to be applied at the full rate.

Speaking on Teagasc’s The Tillage Edge Podcast, entomologist Michael Gaffney stated: “Pyrethroids are still useful; they’re still effective. Our research would indicate that a properly applied, full-rate of pyrethroid will kill a significant proportion of even the partially resistant aphids – Sytobion avenae [grain aphid].”

He added that a survey in 2018 showed 20% of grain aphids in this country have partial resistance to pyrethroids, but resistance levels varied across fields and locations.

Importantly he noted that, at present, resistance is partial, but if the aphid population becomes overexposed to pyrethroids this could move to full resistance where pyrethroids will be largely ineffective.

He encouraged farmers to check for efficacy within five to seven days of the application of an insecticide.

If there is a high population of aphids still present, particularly non-winged aphids which have been present in the field for a long time, then there may be resistance in the population and a second pyrethroid should not be applied. In this situation the farmer should move to alternate chemistry.

Similar to alternating fungicides to reduce the build up of resistance, the same should be done with insecticides where possible or required. However, late sowing can result in no or just one application of insecticide depending on numbers and weather.

An integrated approach is needed when controlling BYDV and farmers should look at all tools available to help. Syngenta recently released the BYDV Assist app which can help farmers to make decisions on aphid control.