Police carried out searches of two Raumanga houses and found about 400 stolen avocados in a garage.
Former NZ avocado grower representative Mike Eagles said he had established a rural neighbourhood watch group over the past few months and growers had been handing over information about thefts and suspicious vehicles to police.
He said about eight orchards had fruit stolen in the raids and some had even been hit four times.
"Some considerable amounts have been stolen so most people are pretty happy to hear about the arrests," Mr Eagles said.
However, he would not be surprised if there were more people involved in the Northland orchard thefts.
"It seems so well organised and the thefts are been done on a very regular basis so there is a market out there for them. They are taking 400 to 500 avocados a night."
Mr Eagles said growers needed to padlock gates and any suspicious vehicles should be reported to police.