Prime Minister Malcolm Turnbull says he is confident the South Australian Liberals will form government at next week's election, calling Opposition Leader Steven Marshall an "absolute vital necessity" to the state.
Mr Turnbull called for an end to the "failed leadership" of the Labor government during a visit to the McLaren Vale wine region on Saturday.
"How can you be in a position where you have the most expensive and the least reliable energy in Australia?" he asked reporters.
"The long and sorry era of Labor government in this state has let South Australians down."
But Mr Turnbull would not comment on the future leadership of the party if Labor were to win a fifth consecutive term at the March 17 poll.
He also skirted questions about whether a ban on foreign donations should be imposed at a state level, similar to the one proposed federally, after Mr Marshall was this week dogged by a rumoured $1.2 million donation from Chinese businesswoman Sally Zou.
"Everyone has to comply with the law on donations, and everybody does - I'm absolutely assured that the state division does," Mr Turnbull said.
The two leaders toured Wirra Wirra winery, where the prime minister rung the harvest bell and crushed grapes in a barrel.
Mr Marshall said business in the region was "booming" thanks to free trade agreements negotiated by the federal government.
He said a state Liberal government would have a dedicated exports minister.
State Labor, who hosted Federal Opposition Leader Bill Shorten last week, downplayed the prime minister's visit during a morning press conference.
"What's the announcement? Where's the money for infrastructure?" Treasurer Tom Koutsantonis said.
"We're only getting two per cent of the nation's infrastructure spend, yet we make up seven per cent of the nation's population."