Three teens jumped a fence into Hollywood mogul James Cameron's Wairarapa hemp plantation, took "selfies" and stole some of the crop - unaware of the crop's famous owner, and that smoking hemp does not produce a high.

Manaea Wilkie, 17, and Mario Bartolic, 18, both of Featherston, and Kaleb Hunt, 18, posed with the hemp plants, taking photos of themselves, police said.

Wilkie took some hemp "heads" to smoke at home to see if they had the same effect as marijuana.

They were arrested as they drove back to Featherston, on March 9.

Wilkie and Bartolic were each convicted and discharged when they pleaded guilty in Masterton District Court yesterday to trespass charges, after lawyer James Elliot said they were two "misguided" young men with "too much time on their hands".

They had since found jobs, he told Judge Peter Butler. Hunt will appear in Rotorua District Court on Thursday.

Speaking outside court, Wilkie and Bartolic said they did not know who owned the plantation, south of Featherston.

Cameron's New Zealand company T Base 2 has a licence from the Ministry of Health to grow industrial hemp, which looks like other, psychoactive forms of the cannabis plant.

It can be grown legally only if it has an extremely low level of THC, the active ingredient of marijuana.

One-year licences can be revoked and the crop destroyed if tests show it has a THC content of more than 0.35 per cent, whereas marijuana has up to 22 per cent.

Police said they were aware of the plantation, as was required under Ministry of Health regulations.

Representatives for Cameron could not be reached yesterday afternoon and his south Wairarapa farm managers declined to comment.

A spokesman for the Ministry of Health said there were 35 operators licensed to grow hemp for industrial or research and breeding purposes. There was only one active, licensed hemp operation in the Wellington and Wairarapa regions.

According to the Soil and Health Association, hemp uses include cooking oil, fibre and a building material.

As well as the trespass charges, Wilkie and Bartolic also faced charges of disorderly behaviour and Bartolic of threatening to injure a female Featherston police officer.

Hunt will also face a charge of unlawfully possessing a semi-automatic shotgun the day after the trespass.

On a separate occasion they were stopped by police and became abusive, police prosecutor Jodie Lawrence said in court, with Bartolic telling the female police officer she would "get what was coming to her" for "harassing" him and his friends.

He later told police his actions were motivated by wanting to earn his Black Power patch.

Wilkie told police he behaved as "a sheep" in following his best friend into aggressive behaviour.

They were initially bailed on condition they did not associate with each other. But they were found together in Featherston on Saturday and spent the rest of the weekend in custody.