The boots and vehicles of a small invading army of seasonal workers could place Northland's $36 million kiwifruit industry at risk.
The region has been in lock-down for several months to try to keep out the kiwifruit vine disease PSA, which last year caused losses in other parts of the country estimated at up to 15 million trays.
Northland is now the only major kiwifruit growing area free of the disease.
The north's kiwifruit growers have united to voluntarily impose stringent hygiene regimes and movement controls on industry players to keep the region free of the disease, but say risk is ramping up again with hundreds of orchard workers due to arrive soon for the start of the picking season - many of them fresh from affected areas, like Gisborne, with earlier picking seasons.
Robbie Bell, chairman of the Northland committee of Kiwifruit Vine Health (KVH), says incoming workers and contractors will be heavily targeted with messages on disinfecting footwear, hands and machinery.
Brad Siefert, KVH biosecurity manager, said the industry nationally was in close touch with places like backpackers' hostels and had prepared waterproof hygiene packs geared for overseas visitors. "A lot of the orchard workers don't speak English so we have kept the data as visual as possible," he said.
"The main thing is to make sure the lines of communication are very clear and open and that nobody is caught short without the necessary information."
Northland's KVH committee had bought and destroyed a large amount of "imported" root stock from garden centres and plant nurseries, which had been extremely co-operative, he said.
The industry had no legal clout but planned to ask the Government to bring in special biosecurity measures, meaning its defensive measures would have legal backing.
A gap in defences might be the kiwifruit brought into the region by the supermarkets.
Northland Regional Authority biosecurity manager Don McKenzie said the potential for infection was there but should be relatively low, as the fruit was washed and refrigerated.
Brad Siefert said the biggest risk was the transfer of plant material from affected areas to orchards.