By Dr Philip Burgess

Lead researcher and consultant,, a partnership of SRUC, James Hutton Institute and SASA

Trials are underway in Aberdeenshire aimed at rethinking the approaches growers take to controlling virus in seed potato crops.

The seed potato sector in Scotland underpins the whole of the GB potato industry, as well as exporting high-quality seed around the world. The natural advantages of the climate, which reduce the numbers of aphids which can carry virus, are well known.

But generally warmer winters – with this last winter being a notable exception – and longer, drier summers are likely to increase the numbers of aphids flying into crops and spreading virus.

There is no doubt that Scotland will remain one of the best places in the world to grow healthy seed potatoes, but some changes in the way crops are managed are going to be needed as the number of pesticides available is reduced ever further.

It is not just that the number of active ingredients is becoming fewer, but resistance of some important aphids is also occurring to those few that remain.

Looking ahead to 2022 and beyond, we can expect further reductions in product availability. A new approach, less reliant on the use of pesticides is required.

SRUC, in collaboration with SASA and NIAB, is looking at new approaches to reducing aphid-borne virus transmission in what might prove to be one of the last AHDB Potatoes-funded projects. Integrated Pest Management (IPM) is the way forward with a number of different methods being used together to control virus spread.

In 2020, a field trial was conducted in Cambridgeshire under very high-risk conditions – the aphid numbers recorded going beyond anything we could reasonably expect in Scotland. In 2021, in contrast, exactly the same trial will be repeated in Aberdeenshire under very different conditions.

These trials include the use of a wheat straw mulch spread over the soil surface after planting. This has been shown to distract the aphids and they move on elsewhere, away from the susceptible potato crop.

In the Cambridgeshire trial, a treatment including the mulch resulted in the lowest virus incidence of all the treatments. A range of IPM treatments were compared to current standard insecticide programmes.

Importantly, in the 2020 Cambridge trial the straight insecticide treatment had no effect on virus transmission.

Inter-cropping, using vetch planted between the drills, was also trialled because evidence shows that if aphids land on other plants before a potato, they can be cleaned of virus and therefore spread is reduced.

Many growers are already using this knowledge and planting purge strips around field margins and in some cases within fields. In the future, we might get used to seeing seed potato fields both surrounded by green purge strips and perhaps interlaced into the tramlines.

These strips might also provide sources of aphid predator species to control the pest within the crop. The net result being that the natural advantages of the environment are enhanced to reduce aphid-borne transmission of virus.

Aphicide sprays, carefully timed and targeted, will remain a necessary tool to control the spread of virus.

However, forecasting aphid flights using historic data and then using within-crop traps (yellow water traps) to understand what is happening in each the field will be essential.

Currently, growers are able to use the AHDB-funded Yellow Water Trap network to monitor what’s happening in their area. It’s a concern that the future of this network hangs in the balance following the ‘No’ levy vote by growers.

As an alternative to traditional pesticides, mineral oil applications have been included in the trial programme.

These have been used in both continental Europe and Northern America to reduce PVY transmission for many years, but only very limited experimental data is available for Scotland.

Regular sprays of oils from very early emergence are being trailed this season. These work by simply covering the leaf with a very thin layer of oil and disrupting aphid feeding. They will need to be applied repeatedly to cover the new and susceptible leaves.

It is always worth remembering that aphids can only transmit virus if they have already landed on an infected plant. The first step in any control programme is to reduce these sources of virus.

Control of ground keepers in the areas where seed potatoes are grown is key to reducing virus transmission, together with early roguing of seed crops to remove as soon as possible any plants growing from tubers infected last season.