Music: Beware - the swamp people are coming

Phil Johnson looks forward to two days of voodoo, spicy food and spicier music as Cajun country casts its spell on London

There might just be time to alert the tabloids and the gents from the Corporation of the City of London before it's too late: on Sunday afternoon there's going to be a genuine voodoo priest holding court in the steamy setting of the Barbican Centre's conservatory. It's not certain what he'll be doing, but it looks suspiciously like black magic on the rates.

As if that weren't enough, there's also to be a Mardi Gras procession around the Barbican lakeside led by so-called Indians, with children invited to make their own outlandish costumes and join in. By Monday, when the focus of the event changes from New Orleans to Cajun and Creole, who knows what could happen. There's supposed to be harmless-sounding workshops in cookery and music, but by sundown there could be a trailer park outside St Paul's and wholesale hog-butchering in the pedestrian precincts. The Barbican's year-long "Inventing America" season might have begun as a polite reaching-out exercise to our cousins across the Atlantic, but all this Louisiana business sounds suspiciously foreign. I mean, some of them don't even speak English.

The culture of Louisiana which the weekend - billed as "The Ultimate Gumbo" - celebrates is foreign even in America, where the deep-south state is regarded by some as only partially civilised. Admitted to the Union as the 18th state in 1812, Louisiana was a French colony until 1762, when it was ceded to the Spanish before being returned to France in 1800, prior to becoming part of the Louisiana Purchase in 1803. Some Americans still consider the $15m (pounds 9.4m) paid for it a bit steep even by today's prices.

While Louisiana's major city, New Orleans, remains partially French in character, the Cajun country around Lafayette to the west is in some ways more French than France itself, and the legacy of slavery has created an equally strong Creole culture that has blended, to varying degrees, with Cajun. Settled by French expatriates from Acadia in Canada (now Nova Scotia) after the British ejected them in 1755, the fiercely independent Cajun traditions of language, cuisine and music still survive in small towns like Mamou, although, since the freeway opened up the swampland in the Sixties, the culture is in decline.

Louisiana's quaint regional customs are looked upon with mixed feelings in the rest of the US. A national TV news special last year exposed the unusual traditions of some of the state's highway patrolmen, who apparently feel they have the right to stop any car with out of state plates and help themselves to whatever cash or property they find. And while it's true that various governors of Louisiana have sometimes been found wanting in matters of ethics or morals, they do make great songwriters. Governor Jimmie Davis wrote that fine old standard "You Are My Sunshine", and in the Thirties the eccentric demagogue Huey P Long penned "Every Man A King", probably the only song by a politician to be covered by Handy Newman (on his great 1974 album about Louisiana, Good Old Boys). You can see Davis's hat and Long's bullet-proof Cadillac in the museum of the wonderful art deco state capital in Baton Rouge, which was also where Long was shot to death. At least he was saved from dying in a car crash, a fate that has befallen a strikingly large number of Cajun musicians.

The Barbican event includes on Sunday's New Orleans day a sold-out concert by Dr John, the remarkable pianist and singer who embodies the city's rich history of rhythm and blues styles, a tradition arguably as important to popular music as the other main musical export, jazz. Now 56, and on a roll since his appearance in the BBC's "Perfect Day" video, with a new EMI record contract and an album yet to be released featuring collaborations with Paul Weller, Supergrass and Spiritualised, Dr John (aka Mac Rebennack) has had more than his share of hard times, as detailed in his picaresque memoirs, Under a Hoodoo Moon (St Martin's Press).

By the time he was 15 Rebennack was working as a session musician, songwriter and record producer in the only real studio in New Orleans, and he thus participated in the tail-end of what was one of the real golden ages of popular music. While the scene had its stars - Little Richard and Fats Domino - much of the best music was made by relative unknowns such as Guitar Slim, Huey "Piano" Smith, Aaron Neville (later of the Neville Brothers), Allen Toussaint and Professor Longhair, Rebennack's piano-man guru. The full story of New Orleans R&B is in John Brovin's book Walkin' to New Orleans.

While it's too late to get tickets for Dr John, the Barbican is holding a free event on Sunday afternoon featuring New Orleans musicians. There's blues from Larry Garner and brass band jazz from the Nightcrawiers (who support Dr John in concert), as well as kiezmer, zydeco (the Creole version of Cajun, usually featuring a man wearing a washboard-waistcoat which he strokes with thimbles), and "weird jazz" from some Sun Ra collaborators. There's also the voodoo man and those pesky Mardi Gras Indians.

Monday's Cajun, Creole and Zydeco Legends day has afternoon workshops in Cajun cookery, dance and music and another free-stage bill of bands, including some from Britain, where Cajun has proved very popular - especially, for some reason, in Derby. The evening concert is dedicated to the most famous of all Cajun bands, the Balfa Brothers, although Burkeman Balfa will be the only survivor from the original group (Rodney and Will died in a car crash in 1979; the genius fiddler Dewey more recently). Headlining is The Balfa Brothers Tribute Band, featuring Burkeman and his nieces Christine and Nelda, who also perform with their own contemporary group, Balfa Toujours. The bill is completed by Creole accordionist Alphonse "Bois Sec" Ardoin, now 83, and the groups of his both his son and his grandson. In Louisiana music is often a family affair.

On Monday the smell of Cajun spices will filter through the Barbican, and the sound of fiddle, accordion and spoons - still the percussionist's choice - will echo off the concrete. By then the voodoo priest will have gone (caught with a chicken in the conservatory and taken off by the Met), and the good times should well and truly roll.

'Louisiana Fest - The Ultimate Gumbo' is at the Barbican (0171-638 8891) on 24/25 May.