Wellington, July 4 NZPA - A Green Party survey shows fruit and vegetable growers face ruin from New Zealand's two giant supermarket chains using their duopoly position to put the growing industry at risk.

Supermarket pricing practices needed to be investigated and a supermarket code of conduct drawn up, Green Party food spokesperson Sue Kedgley said today.

The Greens' survey of 75 New Zealand fruit and vegetable growers found that supermarkets were making huge mark-ups of up to 500 percent on fresh fruit and vegetables, while growers were being forced to sell their produce for less than it cost to produce.

Ms Kedgley said the survey also found that only 15 percent of growers reported that their business ran at a profit, 87 percent of growers were forced at times to sell their produce at less than it cost to produce, and 75 percent of growers thought the supermarket mark-ups on fresh produce were far too high.

"Our survey suggests that unfair pricing practices on the part of some supermarkets are decimating many fruit and vegetable growers and putting their industry at risk," said Ms Kedgley.

"It is simply unsustainable for growers to sell produce on a routine basis for less than the cost of production."

She said New Zealand supermarkets' massive mark-ups on fresh local produce was at the expense of both consumers and producers, as the low prices growers were getting for their produce was not being passed onto consumers.

"Serious questions need to be asked about why supermarkets put exorbitant mark-ups on fresh produce, while mark-ups on processed foods are normally around 2 percent."

Ms Kedgley said it appeared that the two main supermarket chains were using their duopoly position, to play growers off against each other, and drive prices down to unsustainable levels.

"The Government must address the huge power imbalance between two giant supermarket chains and the small-to-medium size growers that are the backbone of our horticulture industry."

Ms Kedgley said there was a supermarket code of conduct and ombudsman in Britain, to ensure growers and consumers were treated fairly, and it was clear one was urgently needed in New Zealand.