Canadian potato farmers have offered a reward of 500,000 Canadian dollars (£255,000) for information about an unknown saboteur.
Farmers on Prince Edward Island say that needles and nails have been pushed into the potatoes as they are grown.
Since the objects first began appearing in potatoes in October, rewards of 50,000 and 100,000 Canadian dollars have been offered with no success.
Recalls of potatoes have already cost farmers millions of dollars.Nails have been discovered by customers in bags of potatoes sold in stores.
The Royal Canadian Mounted Police is investigating and has appealed for anyone who finds damaged potatoes to report them.
The Prince Edward Island (PEI) Potato Board, which represent farmers, has increased the reward for information leading to a conviction to half a million Canadian dollars until 15 August.
Potato farming is the island's main industry and the PEI Potato Board say it is worth over a billion Canadian dollars a year.
The island's farmers have begun installing metal detectors and scanners in an attempt to halt the problem.
'It's food terrorism,' farmer Alex Docherty told the UK's Guardian newspaper. 'The people doing this are cowards, lower than a snake wearing snowshoes. These are really evil people.'
