White rot, long the bane of Gilroy’s garlic-growers, may have
met its match in a new, natural fungicide developed by California
scientists.
Gilroy – White rot, long the bane of Gilroy’s garlic-growers, may have met its match in a new, natural fungicide developed by California scientists.
“People think that urban sprawl stopped people from growing garlic here,” said Bill Christopher, managing partner of Christopher Ranch, California’s largest garlic packer. “But it’s mainly white rot. Once it infects a field, you can’t grow garlic there ever again.”
The foreign fungus infects and decimates the roots of garlic and onion plants, eventually spreading into the garlic or onion bulb, which it starves. It’s named for the white, fluffy growth that erupts from the base of the bulb: the death knell for a garlic crop.
Christopher said “thousands” of acres of garlic had been lost to the fungus, which reached the U.S. from overseas 50 years ago.
Now, one scientist from the University of California, Davis, says he’s found the answer. White rot produces black spores called sclerotia, which resemble poppy seeds and germinate when triggered by sulfuric compounds that leak from garlic or onion roots.
Plant pathologist Mike Davis isolated those compounds, creating dialelle disulfide, or DADS. By injecting them into garlic-free soil, Davis can trick white rot into germinating, only to die when there’s no garlic or onions on which it can feed.
“It’s not lethal to fungus,” explained Davis, “but the lack of food kills it.”
Because the compounds exist naturally in garlic and onion plants, farmers have sometimes used garlic or onion powder, to lesser effect. Others eradicate the spores using methylbromide – a method Christopher said kills most, but not all, of the spores. But a treaty called the Montreal Protocol, signed by the United States, has agreed to phase out the use of methylbromide because of the harmful effect it has on the Earth’s ozone layer, according to the U.S. Department of Agriculture, and is listed as a California Prop. 65 developmental toxin.
“This would be a tremendous boon to Gilroy,” said Christopher, “if it actually works.”
But DADS is still undergoing testing, and might not be commercially available for a year, said Davis. Because it’s non-toxic, the fungicide needs minimal government approval, but Davis is testing DADS to see how it might fit into a farm rotation, combined with other fumigants.
To be effective, the fungicide must be applied at least one season before planting. And though the fungicide is highly effective – Davis estimated between 95 and 99 percent – that might not be effective enough.
“With this fungus, it’s really virulent,” said Davis.
