One thousand acres of Sonoma County farmland likely will be added to a growing quarantine area after the discovery of three European grapevine moths near Calistoga.

Officials on Wednesday received confirmation that the insects were indeed grapevine moths, county Agricultural Commissioner Cathy Neville said Thursday.

The grapevine moth was first confirmed last September in Napa County, where the pest ruined a grape crop. Moths attacked the berries and infected them with bunch rot.

More moths have since been located, and last month the state placed 162 square miles of land under quarantine, nearly all of it within Napa County. In such areas, farmers must ensure they don't spread the moth when moving crops to market.

State rules call for all lands within three miles of an infestation to fall under quarantine. As a result, Neville said, the finds near Calistoga mean nearby lands in Sonoma County will come under restrictions for crop movement.

Last week, officials announced that a single grapevine moth was found near Kenwood, the first such insect to be confirmed outside Napa County. However, a single moth doesn't trigger a quarantine.