Manawatu-Whanganui Regional Council admits that it has not done a good enough job of informing farmers about the rules governing scrub clearance on their properties.
About 40 farmers are being investigated by the council for illegally clearing scrub without resource consent to do so, following aerial surveillance in the area.
The council says the rules have been in place since 2003 and restrict spraying on areas of hill country land of more than two hectares.
Planning and regulatory manager Greg Carlyon says it's important that the rules are well-known and followed.
The council has introduced an instant resource consent process for scrub clearance, which can be granted in the field at no cost.