THE mastermind behind one of Australia's biggest cannabis crops used his young stepchildren as slave labour to tend his fields, killing or torturing their pets to keep the kids quiet, a court has heard.

Michael Bennett Gardner Snr on Wednesday pleaded not guilty to trafficking a dangerous drug in a trial expected to last about two weeks.

In his opening statement, prosecutor Michael Lehane told how Gardner and his wife bought a remote grazing property south of Stanthorpe, in Queensland's southern borderlands, in 2004 and planted vast paddocks of marijuana across hundreds of acres over a period of four years.

His wife and her three children were forced to tend the crops and were given ``shut-up money'' to ensure their silence, Mr Lehane said.

The Supreme Court in Brisbane also heard how Gardner used ``intimidation and violence'' to keep the operation going, pulling the children out of school so they would have more time to work in the fields.

``He was the guiding mind of this illegal enterprise,'' Mr Lehane said.

He described how police found 22,000 plants with a wholesale value of $69 million in fenced-off paddocks when they raided the property in 2008.

An elaborate watering system involving pumps, dams, water tanks and a network of poly pipe spanning 6km had been set up across the property and lookout towers allowed him to keep an eye on the fields, the court heard.

Mr Lehane said police also found a weapons armoury with guns, leg shackles, handcuffs, extendable battons, military grade night-vision goggles and 10,000 rounds of ammunition.

More guns and cash deposits were found hidden in caves dotting the property.

The trial continues.



Originally published as Dad kept kids drug slaves: court told