Landcare Research scientist Hugh Gourlay said recently there could be signs of the beetle's impact on release sites in 20 years, but widespread effects may not be visible for 50 years.
South Otago farmer Rick Cameron said that in the 1980s he and his brother Peter became frustrated at the infestation of Californian thistles on their farm, which smothered about 160ha.
It was so bad Mr Cameron said they had to use truck-tyre tracks as trails to muster lambs.
They trialled several management systems including using chemicals, mowing and hay cropping, with the goal of having an all-grass wintering system.
Mr Cameron said they attacked the problem as they did gorse, a plan that saw them tackle small areas using a mowthen-graze technique.
He suggested limiting control to between 3% and 5% of the farm in one year, then adding a similar-sized area in following years.
Paddocks neighbouring clean areas also had to be kept thistle free.
‘‘It is surprising over time how many clean paddocks add up.''
A key was to ensure pasture in those selected areas was kept clean so it could be grazed for two years and grazed by the best conditioned ewes.
Infested areas were mowed 24 hours before ewes arrived, at a stocking rate of 900 stock units per ha per day.
Mr Cameron said it was crucial to record when they arrived and to ensure they returned to the paddock 21 days later. The 21 days after mowing before stock return was critical, he said.
It meant the Camerons cleaned up thistles in 18 months compared with 24 months when they operated a return grazing time of between 28 and 30 days.
He uses a formula to calculate the 21-day grazing speed: size of area in hectares, multiplied by 900 then divided by mob size.
That translates into a 1200-ewe mob grazing a 4ha area for three days.
Mr Gourlay said the beauty of biological controls was they worked around the clock.
While the beetle could take time to establish and make its mark, he said there had been some spectacular biological control success for ragwort, nodding thistle and St Johns wort.
The biological controls have established quickly and reduced weed infestation.
The thistle beetle feeds on the green foliage leaving little holes. Eventually, it will devour all the foliage above ground and kill the plant.
During cooler months when thistles naturally die off, Mr Gourlay said the beetles would live in the soil as adults, in fence lines or scrub, returning to eat and breed when thistles reappeared.
He said the beetles survived intensively farmed systems, such as rotational grazing in their native Europe, but he suggested farmers create a nursery for the beetle in the first few years after release, leaving areas free of chemicals and mechanical topping.
Another thistle biological control, a weevil, was less resilient than the beetle and Mr Gourlay said it had been slow to breed.