By Dr Andy Evans, SRUC.


This is the year to act to keep potato virus out of crops.

With Covid-19 news all around us, we all are becoming experts in viral disease spread. And we also need to do all we can to protect our seed potato crops from the various aphid-borne viruses.

This is essential to maintain the unrivalled quality of Scottish seed potatoes, particularly in light of the shrinking availability of aphicides for effective virus management.

Maintaining high quality seed health now will help protect future crops as we expect to lose further aphicides over the next few years by reducing the level of virus inoculum available to aphids.

There was an unwelcome increase in the incidence of crops with potato virus Y (PVY) last season, which has increased the risk of virus infected stocks being planted in 2020 and subsequent spread of virus into the 2020 seed crop. But if the industry acts now, problems later down the tracks will at the least be reduced.

The best route to high health seed stocks is through a robust approach that eliminates as far as possible sources of virus before they enter the crop.

A key focus should be on targeting and managing the potential sources of virus:

The mother seed stock – ie, the seed crop planted in the field.

Other seed and ware crops in proximity to the crop.

Groundkeepers/volunteers in potato and non-potato crops.

Potato dumps where haulm growth is present.

Growing seed crops in an environment in which all sources of aphid-borne viruses are kept to a minimum is key. This includes sources within the seed crop as well as outside.

High quality virus-free certified seed should be sourced to minimise the risks of spread from infected plants within the crop. This must be supported by thorough roguing of any virus infected plants and groundkeepers at an early stage – preferably as early in the growth of the crop as practical - before aphid vectors of non-persistent viruses are flying.

There are very good reasons for seed crops to be isolated. But where crops are not completely isolated, the risks from outwith the crop should be recognised.

Adjacent fields should be checked for the presence of potato groundkeepers/volunteers and action taken as appropriate, including informing the owners of these crops on the benefits of groundkeeper management.

Neighbouring ware crops should be as free from virus as possible – the use of untested home-saved seed to grow ware will increase the risk of infection. Remember, you can be forced to burndown heavily infected crops early.

Preventing haulm growth on dumps is also important in limiting the opportunities for flying aphids to pick up virus and carry it into seed crops as well as being an essential part of potato blight control.

Roguing of groundkeepers/volunteers from non-potato crops, and potato plants exhibiting virus symptoms from ware and seed crops is an essential component of virus management in seed potatoes – aphids have to pick up virus from somewhere.

Aphids will acquire virus from the above sources if they contain virus infected plants, and both non-potato colonising and potato colonising aphids play a significant role in PVY transmission. They can pick up the virus in one plant and transmit it to the next in under a minute.

Consider sowing cereal strips at the edges of both seed and ware crops, as they can purge the virus from the stylets of aphids before they move into the seed crop.

There is also a role for a robust insecticide programme and early burndown to control virus in seed crops. However, remember that if you can remove most sources of virus before aphids are active, then these measures will be so much more effective.

We do not know if aphids in Scottish potato fields are developing resistance to pyrethroid aphicides. Samples can be tested free of charge through an AHDB project. Please e-mail who will send collection kits and advice.