Grape growers are being warned to keep an eye out for a fungal disease which appearing in a growing number of vineyards in the Marlborough region.
Powdery mildew commonly affects grapevines at this time of year and in extreme cases can result in crops being written off.
Marlborough Wine Growers chair Clive Jones said most growers were aware of the disease but an increase in incidents over the past two years had prompted a fresh warning to be more vigilant.
"It likes dry, warm conditions and with the last two years being warm and dry, growers have seen more of it."
Mr Jones said a single treatment of sulphur spray was no longer enough to kill the mildew.
"What's happened in the last couple of years is rather than dealing with it once in the season and then forgetting about it for the rest of the season, we've actually seen it recurring.
Even though you've done the initial treatments, it can still come back. The belief is it's actually a sexual phase of the disease that's causing the situation."
Mr Jones said reducing the number of days between spraying was an option to keep the disease under control but warned the plants could build resistance to the spray.