"He then shouted loudly at her 'I'm gunna f ... kill you, you f ... bitch'," Mr Wilson said.
Later in the day he sent threatening text messages to the woman and one to their son which stated, "son get my stuff now or I'm coming with my gun", he said.
When spoken to by police, Mikaera admitted the facts, the court heard.
Previous to this incident, Mikaera was caught with a hydroponic cannabis growing operation being run off stolen power at his Carterton home, Mr Wilson said.
Mikaera had set up a concealed room in a garage at the rear of his house with four growing lights, fans and filter extractors with curtains hiding the operation from neighbours, the court heard.
"He built cultivation pipes and tanks so the plants could be automatically fed and watered. He installed a cable bypassing the power meter into the garage ... therefore none of the power consumed by this operation could be monitored by the power company," the prosecutor said.
Between March 1 and July 31, 2013, Mikaera grew two cycles of cannabis, harvesting them for his own use.
On June 30, this year, he supplied 25 cloned seedlings to someone in Porirua to cover a $2000 drug debt he owed, Mr Wilson said.
On July 31, police located the hydroponic set-up, locating nine mature plants ready to flower and cloned seedlings in preparation for the next growing cycle.
When spoken to by police, Mikaera stated he wasn't a drug dealer.
"He extensively siphoned $6.78 per day in power ... he said he had a reputation of being a good grower," Mr Wilson told the court.
Defence lawyer Virginia Pearson requested the court seek a pre-sentence report including a drug and alcohol assessment before sentencing.
Judge Walsh convicted Mikaera on the charges and remanded him on bail for a pre-sentence report including a home detention report.
He will be sentenced on November 11.
