"We're in our seventies and we could do without this. It's a big knock, a really big knock," Mr Antony said.
"We live an organic lifestyle but we are not against spray altogether."
The Antonys said they were not notified spraying was to take place near to their property.
A NRC inspector visited the property on Tuesday to assess the damage and take plant samples for a chemical analysis. The council is awaiting the test results.
NRC regulatory services group manager Colin Dall said weed spraying in the Northland region was subject to certain rules.
"We are investigating the matter. We will be looking into whether the regulations in our air plan have been met," he said.
Spraying was a permitted activity but rules required written notification for adjacent properties, and public spaces such as schools within 300 metres.
The land in Hewlett Rd was not ''adjacent'' to the Antonys' property but across the road.
Mr Antony and neighbours told the Advocate the smell was very strong, but the other neighbours' garden, about 100 metres away, was not affected.
The Antonys believe the breeze caused the drift to funnel down a dip in the terrain and around the base of the slope at the bottom of which is their garden.
Worst hit were peas, broadbeans and up to 20 grapevines all of which appear to have gone into a burst of deformed growth, and shrivelled at the ends.
The leaves of water lilies on an irrigation pond beside the sizeable garden have curled up, as has carrot grass in an area which the Antonys don't mow outside the garden.
On the advice of a viticulturist, the Antonys must now strip the grape vines of all leaves and bunches of young fruit.
They are philosophical about losing one season's crop but worried there may be lasting damage to the vines, some of which are 20 years old.
One is a heritage pink variety from an old property at Te Kopuru, and given to Ms Antony by her late brother.
The couple make grape juice and give a large portion of their garden produce and fruit to the Salvation Army. They are disappointed they might not be able to give as much this season.
They have also had to disconnect their water tanks until there has been enough rainfall to wash the roof of their house and flush the guttering.