Hi Mary T,
I think this is actually a one-off thing, it is to celebrate the fact the the Lavaux has been given World Heritage status by UNESCO.
The fetes de vendanges which you may be thinking about,take place every year, at the end of September and are actually the following weekend in Lutry , there may be others in Cully etc. There are usually bands/groups playing in the street, perhaps a funfair, parades, and lots of wine and wine caves open

http://www.fetedesvendanges.ch

jo