Ardern responded by saying her father had also worked on the dragline and she doubted her late grandfather would be appalled.
"He was staunch Labour so he wouldn't be turning in his grave."
She said her other grandparents were also farmers in the region and very few would use irrigation so would not be impacted by Labour's water tax.
Ardern was playing up her rural roots at a campaign rally in Hamilton on Sunday, telling them of her upbringing, her experience driving a tractor and saying New Zealand had to address the fact that 60 per cent of its waterways were not swimmable - including a lot in Waikato.
She also denied she had created a rural-urban divide, blaming the National Party for stoking that argument. She said of the 12,000 farms in New Zealand, only 2000 relied on irrigation. Dairy NZ later clarified that these figures refer to dairy farms only.
Downing said the prospect of Green Party policies were especially concerning, such as a tax on nitrates and drastic stock reductions of 30 per cent on farms.
"The Green Party, holy Toledo. I mean when they talk about economics it's just like Hugh Hefner talking about chastity. It's a bloody joke."
Organiser Andrew McGiven said farmers from as far away as Northland, Taranaki and Leeston in Canterbury were expected at the rally where farmers wanted to dispel the perception of them as the baddies for the environment.
A celebrity appearance is expected - Myrtle the tractor, whose last appearance was being driven up Parliament's steps during the 2003 fart tax protests.
McGiven said policies such as new taxes did not only impact on the farmers themselves but the communities they lived in.
"If farmers aren't doing well or if farmers are taxed and lose disposable income, that's going to impact on our small towns."
Many farmers were still recovering from the dairy downturn and returns on wool were also low. There was little recognition of work on riparian planting, fencing drains and waterways and using soaks for run-off.
Downing said farmers knew their work had an environmental impact and many tried to alleviate it. "We've still got more to do, but give us a carrot and not a stick and we'll improve. Taxing us is not going to help."
While few farmers in the Waikato irrigated their farms, Downing said it would hit hard on those in the South Island. The early entry into the Emissions Trading Scheme was also concerning.
McGiven said there would not be a march down the streets - partly because it was a state highway: "The only march we're looking at doing is marching down the road and having a beer. At this time of year, farmers get a bit isolated on the farm and with the weather we've had it's probably as much of a mental health exercise as well."
