One of Whanganui's farming giants is adopting more sustainable winter cropping policies as public pushback against the "spray and pray" technique increases.

Driving down State Highway 4 through the Parapara on October 14, Retaruke farmer and conservationist Dan Steele was appalled at the extent of spraying across steep hillsides along the Mangawhero River. It's the same sight that shocked English visitor Graham Gibbons in January. Steele said there would be more happening, especially in the Rangitīkei District.

The spraying was on Papahaua Station, one of the Atihau Whanganui Incorporation properties, chief executive Andrew Beijeman said. Before it was done the Mangawhero River was fenced off, to prevent topsoil eroding into it.

The herbicide was sprayed from the air, before aerial fertilising and sowing a plantain pasture. The plantain has now run out, leaving weeds and bare patches, and the most recent round of herbicide spraying has been done before the area is sown back to grass.

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The grass will have time to cover the ground densely before the winter rains come, preventing erosion. Steeper areas are being fenced off, for less intensive management.

Such steep slopes will not be sprayed off for plantain or winter crops again, Beijeman said. It's permitted under Horizons Regional Council's One Plan, but the incorporation has decided to limit winter cropping to slopes of less than 20 degrees.

"We believe it's a more sustainable practice."

The policy will be brought in over two years, meaning areas sprayed off this year will come under it.

The incorporation will combine this with best practice grazing - grazing steep country with sheep only and grazing areas near water last, so the standing crop can buffer against soil washing into water.

"If we combine best practice grazing as well as selecting the right paddock we can carry on winter cropping," Beijeman said.

It's the time of year when farmers are making decisions about pasture renewal and winter cropping. There will be other sprayed-off hillsides in the region, Horizons' land manager Grant Cooper said.

Government has been taking an interest in the "spray and pray" technique and in damaging winter grazing, and landowners are watching.

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"There's a lot of interest from landowners to make sure they're ahead of these sort of things, rather than having rules brought down upon them," Cooper said.

Horizons permits "spray and pray" - with conditions. Poplars and willows, and gully vegetation, should not be sprayed, and grazing animals should not denude or compact the soil.

It has talked to people about vegetation that shouldn't have been sprayed, and it may have issued notices but it has never prosecuted, to Cooper's knowledge.

He's about to look at the result of a survey of the region's hill country farmers, aimed to find out how much they use "spray and pray" and how they manage winter grazing.

The council may decide to put more rules around it. If so it will need to change the One Plan - a lengthy process.