(Wine-Searcher) - An Asian fruit fly, capable of infecting grapes with sour rot, is causing concern in Bordeaux.

Bordeaux’s winegrowers face a growing menace in the form of a three-millimetre (0.1 inch) long Asian fruit fly called Drosophila suzukii, suspected of spreading sour rot through ripening grapes in otherwise healthy vineyards.

2014 is the first year both sour rot and specifically Drosophila suzukii, commonly known as the spotted wing drosophila, have been detected in Bordeaux’s red wine vineyards.

“On September 10th, we saw the first symptoms in the Entre-Deux-Mers and certain sectors of Saint Émilion on sandy soil,” said Sophie Aribaud, technical consultant at the Union Régionale Agricole in Grézillac.

While the spotted wing drosophila itself undergoes close scrutiny, the damage remains limited to isolated plots.

“We see a few berries or a cluster infected, maybe a half to one percent of the vineyards,” said enologist Jean-Philippe Fort, part of Michel Rolland’s team. “We prune out the infected grapes and clusters, then do the harvest. The infected fruit is destroyed.”

Sour rot is easy to identify. It smells of vinegar. And it is not entirely unknown in Bordeaux.

Rain falls on an early ripening harvest, the berries burst and the common European vinegar fly, Drosophila melanogaster, arrives, feasting on the juice and laying eggs.

"Sour rot is a very old problem for white wines. I’ve always known it in Sauternes," said Denis Dubourdieu, the eminent researcher, consultant and chateau owner.