With aphid migrations predicted to start imminently in the South of England and two to three weeks later in Scotland, potato growers must adopt a range of integrated pest management measures to minimise the yield and quality-robbing effects of the viruses that these airborne insects transmit.

Viruses such as of potato virus Y (PVY) and potato leaf roll virus (PLRV) – which have the potential to cause significant reductions to the quality, yield and value of seed and ware crops – are carried and spread by a range of aphid species including the peach-potato aphid, bird cherry-oat aphid and rose grain aphid.

These species thrive in warm and dry conditions, when they will actively migrate northwards, carrying with them the potential to transmit viruses from one region to the next.

Young potato plants are particularly susceptible to infection by aphid transmission in the first four weeks post-emergence. Beyond this, mature plants will display a greater or lesser susceptibility to infection depending on their genetics, but even the most naturally resilient varieties will still need to be protected.

While seed crops in the North of Scotland are protected to some extent by the natural barrier to aphid migration provided by the cold peaks of the Cairngorms, growers both to the north and south of the Scottish Border must take additional precautions to stem the spread of infection.

With growers no longer able to rely entirely on chemical controls – due to the increasing resistance of some aphid species to current insecticide modes of action – ProCam recommends that seed and ware potatoes must be protected by an array of control measures to minimise their exposure to disease. We advise the following:

1, Variety, rotation and volunteer management

Where possible, virus-resistant varieties should be used to establish the new crop.

Growers should therefore be wary of multiplying their own seed potatoes from the previous year’s crop as these could already contain a high virus loading. Instead, seed potatoes which have been proven to be ‘clean’ should be used.

Similarly, consideration should be given to the where and when potatoes are planted: late planting can increase the risk of infection – as aphids are more likely to be present while the crop is still young – whilst neighbouring cereal crops and volunteers from the previous cropping cycle will harbour virus vectoring aphids and can add to the potential for virus transmission.

Volunteers should therefore be removed either manually or chemically, as should any virus-carrying ‘ground-keeper’ potatoes from previous seasons.

2, Testing and trapping

Seed lots should be tested prior to planting to ensure they are virus-free, with aphid traps used throughout the season to determine when aphids are present.

Numbers will naturally be much lower in the far north compared to further south, but in both cases the ability to know when the first wave of vectors has arrived will enable the timely commencement of an appropriate aphicide application programme.

3. Chemical controls and the use of oils

Neonicotinoid treatments can be used to provide early protection of seed and ware crops, but as soon as the presence of the first flight of aphids has been confirmed, regular pesticide applications using a range of modes of action, including pyrethroids, should commence and continue all the way through to haulm destruction.

Where appropriate, insecticides can be applied in tandem with blight sprays, with growers advised to seek agronomic advice to determine the most appropriate spray protocol.

Oil treatments, which reduce the spread of viral loadings by preventing aphids from using their stylus to penetrate the leaf surface, can also be used to provide an added layer of protection. It is, however, worth bearing in mind that SASA warns growers to use mineral oils at their own risk due to the risk of scorching.

Whilst there is good evidence to show that oils can reduce the transmission of certain viruses, they shouldn’t be viewed as a panacea as they aren’t effective against all species of aphids.

It is also worth bearing in mind that any yellowing of the crop caused by mild scorching could be falsely diagnosed as an indicator of the presence of disease, subsequently causing the crop to be downgraded or rejected.

4. Haulm destruction

With diquat no longer available, growers are now reliant on the use of protoporphyrinogen oxidase (PPO) inhibitor-based desiccants to destroy the haulm prior to harvesting.

Unfortunately, these desiccants are slower acting than diquat meaning it takes longer to completely destroy the haulm of mature potato plants. This further raises the potential for infection as, until the haulm is completely dead, the risk of virus transfer from aphid to crop remains.

It is therefore essential to continue using an appropriate programme of insecticide treatments right up until the haulm has been completely destroyed.