(UPDATED COVERAGE Dec. 5) Detections of sweet orange scab that began in California’s Imperial County groves have the citrus industry searching for an explanation – and a remedy.

The initial findings were in October in Bard, Calif. Subsequent discoveries included sites in Winterhaven, also in Imperial; and two other counties.

The fungus, which mars fruit appearance but not taste, turned up as well in inspections and tests at Blythe in Riverside County, and California State Polytechnic University, Pomona, in Los Angeles County.

“We were very surprised by the findings in Imperial County, and shocked about the findings at the campus of Cal Poly Pomona,” said Joel Nelsen, president of Exeter-based California Citrus Mutual. “We’re trying to figure out what the sources of those infections are and how best to address it. Do we need a countywide quarantine? Do we need a smaller restricted quarantine area?”

Rind lesions that could render fruit unmarketable even when quality is otherwise intact are a big deal for California growers who send comparatively little citrus to juice processors.

“Sweet orange scab is more critical to us than it is to our friends in Florida, because we’re not juice oriented,” Nelsen said. “We’re fresh oriented and anything that impacts our fresh utilization is bad.”

The biggest effect is likely to be in Imperial County.

“It’s just not a good situation in Winterhaven because we’ve got a lot of fruit there between lemons and oranges,” Nelsen said. “Most of that fruit gets packed in other locales. So we’ve got to set up the right process and ensure we’re not spreading the windborne virus.”

The county has about 6,600 acres of citrus, said Connie Valenzuela, Imperial County agricultural commissioner. Whether a quarantine comes depends on ongoing tests and how far the fungus has already spread, she said.

“Over 500 samples were taken from our county and we’re not the only county,” Valenzuela said. “Probably the quarantine would be the best bet if it isn’t already everywhere. We’re the only citrus-producing state that didn’t have it before it was found in Bard and Winterhaven.”

The detection of the fungus in a university setting at Pomona illustrates uncertainty about causes in particular cases.

“It occurs when you’re adjacent to a highly infected block of fruit,” Nelsen said. “There’s nothing adjacent to the Cal Poly Pomona campus that has citrus. One would think they’re teaching their students the appropriate way to plant a grove and instilling appropriate cultural practices.

“It’s windborne. But you can also get it from bad nursery stock,” he said. “And if it came in via contraband, why were there so many findings when the block itself is supposed to have some significant cultural practices that would impede the spread? For us, the dots aren’t connecting.”