The Manawatu-Wanganui regional council warns it is cracking down on landowners who don't get resource consents before doing aerial spraying on their properties.
The council says the rules, which restrict spraying on areas of hill country land of more than two hectares, have been in place since 2003, but were not widely known about.
The council's consents policy manager, Richard Munneke, says it became apparent landowners did not know of the rules during the hearing for the region's proposed new One Plan, which sets out the regulations for how land is to be used over the next decade.
Mr Munneke says the enforcement is expected to affect all hill country farmers in the Ruapehu district and some in Wanganui and Rangitikei, Manawatu and Tararua.
The council will be carrying out aerial surveillance after the spraying season to ensure landowners in those areas have complied with the regulations.
Mr Munneke says the council is processing consents quickly and will be waiving the fees in order to encourage farmers to contact the council.
He says spraying on erosion-prone hillsides and over streams and rivers has environmental consequences.