The loss of neonicotinoid seed dressings are poised to prove a substantial challenge for barley yellow dwarf virus (BYDV) control in Irish cereal production. The banning of this pesticide has limited the chemical diversity available to growers to control the pest, potentially fuelling the development of resistance among Irish populations.

This is just one of the reasons why growers must take IPM seriously. Growers should first consider the cultural, physical and biological options available to their farming system before filling the sprayer. This was one of the key take-home messages of the 2019 National Crops Forum, which took place on Tuesday.

Aphid resistance

Aphid control and BYDV have become very real issues for growers again in the past few years. A proportion of Irish grain aphid populations now have partial resistance, also known as knockdown resistance (KDR), to the frequently used pyrethroid insecticides. This was first detected in Irish grain aphid populations in 2013.

An investigation into potential KDR in Irish populations was likely inspired by earlier studies in the UK, which began looking for resistant in 2011.

Dr Stephen Foster of Rothamsted Research discussed the UK experience of pyrethroid resistance in their aphid populations at the conference. He explained that analysis of grain aphids captured in a suction trap network throughout the UK showed that the KDR mutation was present at a high frequency (>50%) in some areas, but only as heterozygote.

Sav3 super clone

Due to the clonal reproductive nature of aphids, populations which contain the KDR mutation are likely to have come from the one ‘super’ clone, known as Sav3.

In Ireland, the Sav3 clones are also the most dominant clone found in tillage fields.

KDR is only partially resistant and it is generally accepted that pyrethroid sprays can still kill such aphids when using full rates. However, another mode of resistance, metabolic resistance, was recently discovered in Irish populations.

The loss of neonicotinoids

On 29 May 2018, the European Commission imposed a ban on all outdoor uses of imidacloprid, clothianidin and thiamethoxam.

The industry now faces its first winter season with the loss of the key ingredient (clothianidin) to the insecticide dressing Redgio Deter.

Speaking about this loss, Dr Foster was quick to point out that growers could end up using more foliar sprays, leading to increased water usage, increased costs, the development of further resistance and ultimately the loss of yield and income.

IPM measures

There are a number of basic aphid control measures which should be adopted this season. Teagasc’s Ciaran Collins explained that sowing date had one of the biggest impacts on the likelihood of BYDV infection through aphid transmission.

Where possible, he stressed that delaying drilling will help decrease aphid pressure and subsequent chances of infection.

He also stressed the need to look closely at rotations, ensuring to have a suitable break crop in the mix which will also help reduce pressure. Equally, care should be given to limit the green bridge (stubble, volunteers, covers) created between cropping years.

Ultimately, however, in order to preserve the efficacy of pyrethroid chemistry and halt the development of resistance, growers will need to spray less. This means using the above control measures, but also being selective in where they apply the chemical.