Hawke's Bay Regional Council is investigating a complaint that drift from a herbicide spray has severely damaged two vineyards north of Napier.
The Howard and Grapeview Farm vineyards say 24-D, which is used to control broadleaf weeds in pasture, drifted over their grapevines in late September.
The spray has wiped out most of their grape crops for this season and could mean the vines will have to be pulled out and replanted.
Regional council compliance manager Bryce Lawrence says any number of people could have used the spray during that time.
The council has rules for the use of 24-D under the Resource Management Act.
Purchasers of the product require a dangerous goods licence.