Dairy sprays protect grapevines from powdery mildew.
Milk could be used to make organic wine. Sprayed on grapevines once a fortnight, milky water seems to control powdery mildew as effectively as sulphur and copper fungicides, without tainting the grapes' taste.
Peter Crisp of the University of Adelaide in Australia made the discovery during his survey of traditional treatments for the fungus, which currently costs the Australian wine industry A$30 million (US$16 million) a year.
"Most of them did not provide good control," he says, "but milk and whey stood out."
The fungus can engulf whole grapes, rendering them unfit for wine-making. Sulphur sprays stop powdery mildew growing by interfering with its enzymes. How milk works is not clear, but full-fat seems to work best.
Milk fat or whey protein may feed microorganisms on the vine surface that then compete for space or even consume the mildew spores, says Wayne Wilcox, a plant pathologist at Cornell University, New York.
“There was a level of disease that some growers would not find acceptable Wayne Wilcox , Cornell University New York”
"There is definitely something in the treatment, but I would like to see more data," says Wilcox. He recently visited an Australian vineyard that was experimenting with milk treatment. "There was a level of disease that some growers would not find acceptable," he warns.
Reducing sulphur treatment is important to organic wine-makers. "Having an organic farm spraying sulphur seems a bit odd," says Will Davenport, director of UK organic-wine producer Davenport Vineyards. Standard fungicides can harm the insects and soil bacteria that keep other pests down.
However, vegans could not drink milk-treated wine. So Davenport makes 'compost tea' to control the powdery mildew on his farm. This liquid compost is full of soil bacteria, but contains no fungal spores. Sprayed on a vine, the bacteria cover the plant's leaves, competing with, and eating, the fungal spores.
Cornell University New York