Delayed sowing a tool in the fight against BYDV

Barley yellow dwarf virus (BYDV) can cause a loss of up to 3.7t/ha in winter barley. The virus also has the ability to affect wheat, oats and spring cereals.

Ciarán Collins – Teagasc tillage specialist – was speaking on BYDV management at the Teagasc National Crops Forum yesterday, September 10.

As farmers now look into a winter sowing season without Redigo Deter – a neonicotinoid seed dressing banned in April 2018 – they must now look to other methods of aphid control, as a large population of the pest currently carries resistance to pyrethroid products used in their control.

That pyrethroid is the last line of defence in the control of BYDV.

Farmers must first look at the sowing date. Delayed sowing can decrease the risk of BYDV as aphid numbers decline into the winter and colder weather.

Getting the balance right between delaying sowing and drilling into an appropriate seedbed is the hard thing to do.

Rotation is another tool which can be used in reducing BYDV levels. Moving away from continuous cereals can see a decline in BYDV levels.

Greater risk of pyrethroid resistance

Work from Lael Walsh in Teagasc Oak Park showed that the chance of having aphids resistant to pyrethroids is eight times greater in continuous cereals than in rotations with beans or oilseed rape, for example.

Lael’s work also showed that the risk of finding resistant aphid’s was 1.4 times greater in early sown cereals compared to later sown cereals.

Where two pyrethroid sprays were applied, rather than one, there was a 1.7 times greater risk of finding resistant aphids in a crop.

Green Bridge

Ciarán added that the destruction of a green bridge cover between crops can result in a significant reduction of BYDV.

However, this is easier said than done, as its implementation may mean the destruction of a green cover used to take up nutrients over winter and protect the soil, as well as improving soil structure.

Forecasting

When deciding on a BYDV control strategy farmers must consider weather. Sowing early means crops will most likely be exposed to more mild weather which is suitable for aphid activity.

The use of suction cups to measure aphid numbers may also be useful, but may not be practical on-farm. Site history and location should also be considered.

Site history may take in rotation data, while coastal locations may be more susceptible to the virus as the weather may be milder.

Work by Teagasc has shown that BYDV levels have been elevated in coastal locations.

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