Police are urging farmers and rural residents to report any suspicious activity that may be linked with cannabis growing.
Waikato Police say the cannabis harvesting season has finished and cultivators will be returning to renew their plots.
Police expect a spike in farm-equipment thefts, livestock disruption, and trespass by people putting in cannabis plots.
They say there's a growing trend of cannabis growers laying traps around the plots and arming themselves.
Farmers are advised not to approach trespassers, but to call the police.