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— At Bernardo Winery, one of the oldest olive oil producers in California, oil flow has come to a standstill. While the Rancho Bernardo company has historically produced 300 to 400 gallons of olive oil per year from its 1200 trees, the olive fruit fly, an invasive pest that’s native to Mediterranean Europe and north Africa, has already destroyed this fall’s crop, says company director Rossi Rizzo. The female insect does not kill the tree but bores a hole in the developing olive, where she lays a handful of eggs. She may then go on to lay several hundred more in successive olives. Throughout Southern California the insect’s maggots have wrought havoc on the olive oil industry.

Gary Bender, farm adviser with the University of California, Davis extension office in San Marcos, worked with Bernardo Winery near the turn of the millennium, just a year after the fruit fly’s New World arrival, in an attempt to control the insect.

“We did a trial run with some pesticide applicants. We treated every tree every other week, and we achieved some control, but not enough for commercial use. We reduced the maggots from three or four per olive to about one. In the end, they just threw out the entire crop.”

While still a baby in the global olive oil market, California has surged as an oil producer in the past ten years. The state’s growers churned out half a million gallons in the fall and winter of 2007. This season, 750,000 gallons will go to bottle. Five years from now, the experts say production will hit 5 million gallons, and by 2020, 20 million gallons. Americans currently consume 70 million gallons of olive oil each year, over 99 percent of which is imported.

California’s olive oil industry is centered in the Central Valley, but scattered entrepreneurs in the San Diego area are entering the market. Chef Eric Edney, owner of a Taste of Florence in Escondido, purchased a five-acre grove of Frantoio and Leccino olives in Valley Center two years ago. Most olive trees begin producing fruit at three to five years of age, and Edney’s six-year-old trees produced their first harvest in the fall of 2007. The entire crop, however, was wormy. This year, Edney has set insect sticky traps and regularly applies an organic poison derived from sugarcane, which the flies readily devour. Thus far, the measures have kept the fly at bay, and Edney expects to mash out 300 gallons of oil in late October, with which he will supplement his restaurant’s annual consumption of 600 gallons.

Edney believes the olive, which requires a relatively small amount of water to thrive, could be the fruit of the future in San Diego’s arid environment.

“Water’s going to be an issue in Southern California,” he says. “It already is. It’s a desert here. There’s no way around it. These huge citrus and avocado groves are feeling the pressure of water cuts, and olives are an obvious substitute.”

The fruit fly, however, must be controlled.

The pest is believed to have first appeared in North America in Los Angeles in 1998. How it arrived is not known. It has since impacted the Baja olive industry east of Ensenada and spread into Northern California as well, though its impact has been minimal in the Central Valley, where high summer temperatures can deter the insects. Vincent Lazaneo, urban horticulture advisor with the UC Davis extension’s San Diego office, says that nonharvested trees on private property are perpetuating and maintaining the olive fly’s presence. Each autumn, such trees bear fruit that falls to the ground unpicked. Left to rot, the olives provide prime overwintering habitat for the insects, which essentially hibernate through the colder months.

“Residential landscape trees are the problem,” Lazaneo says. “It’s feasible to control the insect, but you need to be isolated from those unpicked trees.”

In commercial situations, the complete harvest of a region’s olives each year can effectively curb the fruit fly population, believes Thom Curry, owner and oil maker at Temecula Olive Oil Company, in Riverside County.

“If more people around here just picked their olives, it would be less of a problem,” he says.

Curry has successfully protected his own 50 acres of olives using traps and sprays — the same used on Edney’s orchard — and he additionally manages 100 acres of private groves in San Diego, Orange, and Riverside counties, producing all told 4000 gallons of extra-virgin olive oil each year from more than 30 olive varieties.

“Extra virgin” is the highest grade of olive oil and is defined as such by industry standards. The California Olive Oil Council oversees about 80 percent of in-state production by a voluntary certification system. Its members, about 250 oil producers throughout California, submit samples of each year’s harvest for analysis. Laboratory testing measures free fatty acid levels, which must stand at no more than 0.5 percent if the oil is to qualify as extra virgin. Acidity results from oxidation of either the olives or the oil. Bruising and fruit fly damage can produce high acid levels too. Oxidation is further checked with an ultraviolet light test and by measuring peroxide levels.

Oils that pass the acid test must then pass the inspection of a tasting panel, which looks for the desired qualities of fruitiness, pungency, and bitterness. Earthiness is considered a defect, and occasionally the panel, which meets monthly in Napa, comes across an oil that has been pressed unknowingly from fly-infested olives.

“Those oils taste like maggots,” says Curry, a tasting panel member.

Oils that qualify are labeled with a stamp reading “California Olive Oil Council Certified Extra Virgin.” Growers who are not members of the council may label their oils as extra virgin without any panel analysis, though a brand-new law, signed into effect by the governor at the end of September, requires that all olive oils sold in California be labeled in accordance with the standards of the International Olive Council in Madrid. Thus, marketing low-quality olive oil as “extra virgin” is now illegal in California, regardless of the oil’s place of origin. Many millions of gallons of fraudulent oil — often blends of soybean oil, low-grade olive oil, and beta-carotene for flavoring — are shipped to the United States each year, much of it from Italy. Labeled “extra-virgin olive oil,” this product may sell for $6 to $10 per liter. Bernardo Winery’s extra-virgin olive oil, by contrast, has sold for $28 per 375-milliliter bottle. Assenti’s Pasta on India Street in Little Italy carries a dozen Italian extra-virgin olive oils that range up to $28 for a liter. Coowner Luigi Assenti warns consumers that price can be suggestive of quality.

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a2zresource Oct. 15, 2008 @ 12:58 p.m.

Regarding ornamental olive trees, the University of California's integrated pest management website recommends using a plant growth regulator applied directly to flowers, causing them to fall off prematurely. This should help to prevent a fruit fly maggot infestation and at least locally interrupt their life cycle as an undesirable pest.

Agricultural growers would be appreciative.

More details at:



JulieParrots Nov. 9, 2008 @ 4:21 p.m.

Thank you a2zresource for providing the pest notes pertaining to the olive fruit fly, I just read all of the link you provided. Now I'm just wondering if it's even worth the extra money to spend on a "higher-grade" bottle of E.V.O.O. which is supposed to be "healthier than corn, soybean, and vegetable oils.


JulieParrots Nov. 9, 2008 @ 4:26 p.m.

D'oh!! I had just finished eating a bowl of pasta with E.V.O.O. before I read that link. I hope I don't get flies in my belly now :(


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