Three vineyards have had grapes and even whole vines stolen since mid-September, police told AFP on Wednesday.
They said about six and a half tonnes of grapes disappeared from a vineyard in Genissac near the world-famous Saint Emilion region, adding that the theft was clearly committed by professional vintners.
Between 600 and 700 kilogrammes (1,300 and 1,500 pounds) of grapes were stolen from a vineyard in Pomerol, which produces top quality reds.
Thieves also uprooted 500 vines from a vineyard in nearby Montagne, police said.
A fourth grape robbery took place in Lalande-de-Pomerol, according to a local press report.
Thieves making away with grapes is not a new phenomenon but it has surged this year apparently because of a disastrous yield.
“There's a great temptation to help oneself from (the vineyard) next door,” an industry expert told AFP on condition of anonymity.
France faces its poorest wine harvest since 1945 after an unusually mild March and frosty April, experts said last month, although a hot summer promises to deliver top vintages.
The agriculture ministry said output was expected to total 37.2 million hectolitres (983 million US gallons), 18 percent less than 2016 and 17 percent below the average over the past five years.
The 2016 harvest was already one of the poorest in 30 years.
This year, bitter cold struck twice within a week in April, ravaging the fragile shoots and buds that had emerged prematurely following mild temperatures in March.
To combat the frost, nervous Bordeaux winemakers set fires in oil drums, then positioned them carefully between the rows of budding grapevines. Giant fans were also deployed to battle the cold, damp air settling on the plants.
At the prestigious Vinexpo wine fair in Bordeaux in June, winemakers brainstormed over how to mitigate challenges to their livelihood posed by climate change.