While thefts from market gardens happened frequently, information was seldom passed on to police, he said.
"I think there is often a lot of theft from market gardens that goes unreported because the amounts are difficult to detect, and it's people helping themselves to fruit and veges because they can. But, it's rare to have something that's taken on a commercial scale reported to us".
He advised retailers to ensure produce they bought was obtained legally.
"We would encourage everyone that has a businesses that deals in produce that if a deal does not seem right or too good to be true, to ask questions of the seller to establish they are legitimately in possession of what they are trying to sell".
At the time of the Kakanui incident, Mr Grant advised growers in the area to be vigilant about security and to report any suspicious activity to police and fellow growers.
Oamaru Organics farm manager Nigel Clark said his farm, which grew a range of produce, had not been targeted, but he knew the land was not immune to theft.
"We've been really lucky to be honest ... let's keep it that way.
"You would have to know what you were doing. Even for someone to come on our farm, how do they know that the spuds are actually ready? Or that the lettuces are ready? It's a bit different to someone walking into your shed and stealing a chainsaw or something".