Orchardists growing gold kiwifruit may have had their hopes of bonanza returns this season dashed as they wait on scientific confirmation that a vine-killing bacteria - which hits gold kiwifruit particularly hard - has established in New Zealand.

Hundreds of millions of dollars worth of exports could be at risk, the industry says.

Biosecurity New Zealand has not disclosed the location of the incursion, but its response manager David Yard said tonight diagnostic testing had tentatively confirmed the bacterial kiwifruit vine disease, Pseudomonas syringae pv actinidiae (PSA), has been found on vines in a North Island orchard.

"The diagnostic testing ... we're now 95 per cent certain that it is the particular bacteria that causes this disease," he said. Once the diagnosis was confirmed, biosecurity officials would decide what action to take.

The orchard grows Zespri's Hort16A gold kiwifruit cultivar and movements on and off the property are restricted, as plant disease experts visit other orchards surrounding it to work out whether the disease has spread.

Two listed kiwifruit companies at Te Puke, Seeka Kiwifruit Industries and Satara Cooperative Group, today sought a trading halt on the NZX because of the generic risk the disease potentially poses to the industry as a whole.

The disease has not been found on orchards directly belonging to either company, but they have a good insight into the damage some strains of the PSA bacteria can cause.

Seeka chief executive Michael Franks is a director of Opotiki Packing and Coolstorage Ltd (Opac), which in April told shareholders the canker threatened to financially wipe out its 84ha gold kiwifruit orchard in the Lazio region of Italy. Opac said its Newgold orchard - valued at $7.16 million in December 2008 and producing a million trays a year - should be written off.

New Zealand scientists have suggested a colder winter than normal combined with a wetter spring than usual can trigger a surge in infections.

Zespri chief executive Lain Jager said that an orchardist brought in consultants when he noticed a symptom of leaf-spotting on his vines, and the consultants brought in experts from state science company Plant and Food, who raised the spectre of PSA last Friday.

One difficulty was the possibility that the bacterial disease could be spread by bees being put into orchards to pollinate crops.

A strain of the bacteria wiped out 50 per cent of the "gold" kiwifruit vines in one Italian region last season.

If that happened in New Zealand, the potential cost could be "hundreds of millions of dollars".

And some countries, such as China - which takes 7 per cent of the NZ exports - could restrict access to their market on grounds of disease risk.

The two listed companies will advise shareholders tomorrow about the potential impacts on their earnings. Seeka - which controls 26 per cent of New Zealand crop - last traded at $3.10, and had lost 1.6 per cent in value this year.

Satara, which is listed on the alternative index, last traded at $1 before the trading halt. Its share price has risen 42.9 per cent this year, with details of a proposed merger with EastPack expected in mid-November.