Potato mop top virus could well be here to stay.

Potatoes New Zealand and Biosecurity New Zealand say the disease cannot be eradicated and will have to be managed instead.

In its most recent stakeholder update on the virus, the Ministry for Primary industries said its chief technical officer had removed the Unwanted Organism status for the potato mop-top virus after advice from MPI scientists and discussion and agreement between Biosecurity New Zealand and Potatoes New Zealand.

"It has now been agreed that MPI will transition the current response into an industry-led management programme for PMTV, whilst still supporting the industry to achieve agreed outcomes.

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"Biosecurity New Zealand is continuing testing to identify how far spread potato mop top virus is. The number of farms under suspicion of having the virus changes regularly, as we rule properties out, or identify potential new properties."

The update said four Canterbury properties had been confirmed to have the virus.

Further testing, including soil testing, was being undertaken to determine whether 10 additional farms are infected with the virus, not 18 as earlier reported. Soil testing takes a number of weeks to complete.

MPI said the virus was not a food safety issue.

The first infected potato was found during routine sampling of material at a chip processing facility.

Biosecurity New Zealand and Potatoes New Zealand launched a joint response on September 19.

The virus, which causes distortions to the potato skin, deep cracking, rust-coloured arcs and streaks in the tuber flesh, is spread by soil-borne fungus but survives long-term in the potato plant or fungus. If established in fields, its spores can survive up to 20 years in the soil.

Biosecurity NZ said if widespread, it could cause productivity issues for growers.

Anyone with a symptomatic potato please call 0800 80 99 66 or email PMTV2018Liaison@mpi.govt.nz