Avocado thieves are targeting orchards in the Waikato and Bay of Plenty armed with rakes and duvets.
Jen Scoular, CEO of NZ Avocado, says they are aware of 30 to 40 instances of avocados being stolen from orchards in the middle of the night.
Some orchardists are losing as much as a quarter of their crop for the year.
"They will come in apparently with utes, they drive into an orchard, they put a cloth out or a duvet cover out, they literally take them from the trees and then throw them into the back of the ute and drive off."
Most of the stolen fruit will end up at small grocers or at farmers' markets, since major retailers require a maturity certificate.
"I’ve heard of one case at a sushi shop where somebody came in with a crate of bright green avocados, and they just won’t ripen."
Ms Scoular says the best way to check if the avocados for sale are stolen is to look at the stalk.
"At this time of the year, they won’t have their stalk, or the stalk will be really long. We have a 3-5mm stalk that has to be when the fruit are harvested properly.
"They’re also likely to be really bright green, they are very unlikely to ever ripen."