UC scientists are testing a fungicide aimed at reversing California's dramatic decline in garlic production.

The problem is "white rot," a rapidly spreading, persistent soil fungus that destroys garlic, onions and related plants. Statewide, growers have abandoned garlic production on more than 13,000 acres of prime farmland in the San Joaquin Valley counties of Kern, Kings and Fresno. In Gilroy, the Garlic Capital of the World, only 500 acres remain in cultivation.

However, a commercially developed natural fungicide, tested in recent years by UC Davis plant pathologist Mike Davis and other UC scientists, has proven to be 95 percent to 99 percent effective in controlling the virulent fungus. The garlicky-smelling, sulfur-containing compound known as DADS, for diallyl sulfide, is found naturally in garlic and onions. It acts as a biostimulant when applied to the soil, tricking white rot into germinating. Then, in the absence of a crop, the fungus quickly dies.

"I'm optimistic that this fungicide will enable growers to produce a profitable crop on infested fields," Davis said. "The next phase of our research, a demonstration project beginning this fall, will focus on how this compound performs in a commercial field."

The state Department of Pesticide Regulation awarded a grant to Davis for his initial research, and recently announced funding for a two-year project to demonstrate how DADS can be used in growers' fields in combination with other fumigants.

John Stumbos is a writer for the College of Agricultural and Environmental Sciences.