The Australian Wine & Brandy Corporation has said it expects the 2007 harvest to be down 35% this year.
Following a year of frosts, droughts, fires and locust plagues, winemakers last month predicted the vintage would fall 30% but figures released this week showed it was worse than expected.
"Seasonal conditions are reducing yields to a 30-year low," said Lawrie Stanford, the Corporation's manager for information and analysis.
"Given the past three harvests were above average this is some compensation," he added.
Red wine will be hit harder than white wines, with yields down 40% and 29% respectively.