Border checks will be in place by March to test for genetically engineered material in imported seed shipments.

 Until now there has been no compulsory testing of imported seeds for GE contamination.

The New Zealand move comes at a time when there are no international standards for quality assurance or border tests.

 New Zealand officials have just finished dealing with a shipment of imported sweetcorn seed that was thought to contain GE material.

Initial testing suggested there might be minute traces of GE contamination, but a more detailed evaluation could not detect any such material, said the Minister for the Environment Marian Hobbs.

"Our best advice is that it is not possible to establish a testing regime which would provide absolute certainty that a batch of seed is GE-free."

She said achieving absolute certainty would require every seed to be tested and the only way to eliminate the risk would be to ban all seed imports from countries growing GE crops.

She said the Government planned to allow a low level of accidental contamination, such as 0.5 per cent in shipments of maize and sweetcorn seed, using a test sampling system.

These border checks will affect New Zealand's cropping farmers, who import 186 tonnes of corn seed each year. About 161 tonnes of this comes from the United States, where some farmers and grain handling companies have been found to have been mixing conventional and GE corn crops.

New Zealand imports maize, sweetcorn, tomato, squash, canola and a small amount of soybean seed from countries that grow both GE and conventional seed.

Green Party co-leader Jeanette Fitzsimons said the contamination scare came after a company with export orders for GE-free corn tested its imported seed.

She said the order was an indication of a growing market for food crop seeds from countries that did not grow GE crops.

But Ms Hobbs said an outright ban on seed imports would cost New Zealand farmers and horticulturists an estimated $100 million a year.

It would also affect the extensive trade New Zealand had in "bulking up" newly developed cultivars for Northern Hemisphere companies wanting to get two crops off the same seed line in one year.

This business, largely based in Canterbury, is estimated to be worth $30 million a year.

Guidelines for New Zealand's sampling and testing procedures are being developed by the Ministry of Agriculture and Forestry and the Environmental Risk Management Authority.

"We recognise this is a conservative approach and we will be looking to the Royal Commission [on Genetic Modification] for advice in its findings on how such issues should be treated in the future," said Ms Hobbs.

The interim standards are to be established by March, which is when orders for the next growing season are expected.

Ms Hobbs said the standards could be reviewed if any changes were needed after the royal commission reported in June.