Hawke's Bay Regional Council is urging landowners wanting to kill thistles and broadleaf weeds, to use hormone sprays before pip and stone fruit trees and grapevines burst into bud.
The council does not want a repeat of last year when an award winning grape block north of Napier was severely damaged.
It says spraying should not be done on a cool still day, as it increases the risk of spray drift.
The council says there are simple rules people should follow, including following the directions on the label and making sure spray equipment is well maintained.
Hawke's Bay Winegrowers vice-president Xan Harding says hormone spray damage is devastating for grape vines and can cause a whole crop to be lost or in more serious cases, can kill vines.
Meanwhile, Bay of Plenty Regional Council is warning kiwifruit growers to take extra care when applying sprays over the next few weeks to promote budding.
Pollution prevention manager Nick Zaman says orchardists must notify their neighbours, put signs on the road verge and not spray in strong winds.
He says spray drift can damage crops or plants that are not being targeted, as well as causing skins rashes, headaches and breathing difficulties.