Emergency application granted against potato viruses

An emergency approval has been granted for paraffin oil product Olie-H in seed potato crops – helping growers tackle non-persistent aphid-vectored viruses.

Non-persistently transmitted potyviruses – sometimes called mosaic viruses – are the most problematic viral diseases affecting British potato production. Currently, the dominant species is potato virus Y (PVY).

PVY is most damaging in ware crops grown from secondary infection of seed. Depending on the variety, affected plants can lack vigour, producing smaller and sometimes misshapen or cracked tubers.

When aphids probe the leaves of plants infected with PVY, they can pick up the virus on their stylet or mouthparts. The disease can be transmitted quickly – within minutes or even seconds of probing an uninfected plant.

This in contrast to persistent viruses like potato leaf roll virus (PLRV), which take much longer for an aphid to acquire and become infectious.

Aphids that colonise potato crops – such as the peach-potato aphid – are key to its transmission, say experts.

Welcome news

VCS Potatoes agronomist Graham Tomalin, who oversees seed potato crops across East Anglia where PVY is a significant threat, said news of the successful application was a welcome boost for growers.

“It’s been an excellent team effort to gather all the evidence on the risk posed by PVY in British seed production and make a case for the emergency approval.

“Olie-H is a useful addition to integrated pest management (IPM) strategies, with a broad range of measures key to lowering virus levels – and maintaining good seed potato health.”

Rapid transmission

Non-potato colonising aphids like the grain and willow-carrot species, as well as colonising aphids, can spread PVY quickly as they move through crops.

This wider range of vectors and speed of transmission make it hard to manage. Key vector species have developed resistance to pyrethroid insecticides – including to their rapid ‘knock-down’ action – so it has only become trickier in recent years..

Mineral oils

Applying mineral oils as adjuvant scan manage PVY. These work by coating the crop’s leaves with a thin film, which disrupts the acquisition and transmission of virus by the aphid’s stylet.

Certis Belchim UK potato crop manager Caroline Williams said that until now mineral oil products have only been permitted from emergence up to tuber initiation (BBCH 40) in seed potato crops.

This led to the  emergency application for Certis Belchim product Olie-H to be used from tuber initiation onwards. Applicants were Horticulture Crop Protection, Seed Potato Organisation, GB Potatoes, SAC Consulting and VCS Potatoes.

Ms Williams said: “The successful application means seed growers will benefit from the proven efficacy of oils for the entire growing season in 2024, helping suppress non-persistent virus levels in seed stocks.

“We recommend that Olie-H is always applied to a dry leaf and growers avoid applying it in the heat of the day. It’s also best used as part of a virus control programme containing translaminar insecticides like Teppeki and InSyst.”

Emergency approval – key points

Olie-H attributes

• Suppresses transmission of non-persistent virues like PVY

• Works by coating leaves with a thin layer of oil

• Oil reduces the likelihood that the aphid’s stylet (mouth parts) will pick up the virus as it probes an infected leaf

• Unlikely to control persistent viruses like potato leaf roll virus (PLRV)

Label information

• Maximum individual dose 6.25L/ha

• Maximum of six applications per season   

• First application from BBCH 40 (tuber initiation)

• Spray interval 7 days between applications

• 18m buffer from surface water

• 3-star drift reduction nozzles must be used

• Minimum water volume 200–400L/ha

Stewardship requirements

• Applications timings and growth stage must be recorded

• Always follow the product label