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News: 05/15/2015

Community effort to combat the olive fruit fly

A widespread pest you’ve never heard of

An olive fruit fly. Source U.C. Riverside, provided by Marshall Johnson.

Overripe olives can be a problem for more than just your driveway. They may be creating a home for the olive fruit fly, a well-established pest that seems to be spreading in Sonoma Valley.

The olive fruit fly was first discovered in Southern California in 1998 and has since spread state-wide, arriving in Sonoma County in the mid-2000s. A small brown fly that lays its eggs inside the olive skin, the olive fruit fly was introduced from the Mediterranean region where it continues to wreak havoc on olive harvests today. Last year, parts of Italy famed for olive oil, like Umbria, were hit particularly hard by the olive fruit fly and it was reported that close to half of the frantoi (olive crushing plants) in Umbria did not open at all.

Locally, growers in both Sonoma and Napa valleys have reported ongoing problems controlling the pests, although estimates of the infestation are still much lower than in Europe.

“It is a geographic infestation that really varies, but they are going everywhere now,” said Don “The Olive Guy” Landis, who runs olive workshops throughout the North Bay. Landis, who picks from about 30 olive trees scattered throughout Sonoma and Napa valleys, said he’s stopped picking in some places because the infestation was so bad the yield wasn’t worth the effort.

Both Beltane Ranch and Benziger Winery in Glen Ellen wage their own annual battles with the fruit fly. Jeffery Landolt, viticulturist for Benziger Winery said that they are constantly trying to protect their 1,000 olive trees, but have seen an increase in the flies over the last two seasons, possibly due to the drought having an impact on the fruit flies’ natural regulators.

“Our system here is in good balance and we are a bit elevated from the valley floor. Because of these two things, last year we didn’t have the same pressure from the pest that other folks in the Sonoma Valley had. However, this year we are seeing and hearing that the pressure is going to be even worse so we are employing both fly traps and organically approved bait/attractant to decrease the overall numbers of the fly,” wrote Landolt in an email.

According to reports by U.C. Davis’s Statewide Integrated Pest Management Program: “In areas of the world where olive fruit fly is established and not controlled, its damage has been responsible for losses of up to 80 percent of oil value because of lower quantity and quality, and in some varieties of table olives, this pest is capable of destroying 100 percent of the crop. Some European districts cannot grow table olives because control of olive fruit fly is not economical. The expense of treatments and the likely crop damage have the potential for eliminating olive culture in home orchards or as a viable commercial industry in California.”

California produces 99 percent of the olives grown in the U.S. Sonoma County grows more than 400 acres of olives, according to the most accurate crop figures from the Sonoma County Department of Agriculture, for a total value over $276,000. Sonoma County, like many others, has its own pest detection program that places traps in urban areas from May to October to detect the presence of tropical and exotic fruit flies. Officials said these traps confirm that population of the olive fruit fly was significantly higher in 2014 than in past years.

Large-scale growers are already well-aware of the damage the olive fruit fly can do, but hobbyists or homeowners who have no interest in harvesting their olives may be unaware that they are contributing to the problem. Female olive fruit flies have a several-mile radius so even one fruit-bearing olive tree planted for landscaping or beauty may become a home for the pest if the fruit isn’t picked or protected. Also, because the olive fruit fly can lay its eggs during many stages of the olive fruit lifecycle, the fruit fly can have three to five generations per year depending upon local conditions.

According to Landis, the infestation seems to be getting more widespread because the Sonoma Valley climate is hospitable and there are a large number of olive trees not being cared for, creating a prime breeding habitat for the flies.

Olive tree owners can resort to using the same kinds of traps and sprays used by large scale growers. The most widely-used trap is the McPhail trap, which uses yeast tablets to attract the olive fruit flies. There are also organic options that are better for the environment, but these can be time consuming and expensive. If a tree owner doesn’t want the fruit, Landis said, the best option is just to remove the tree. For those who still like the look of the foliage, fruitless olive trees can be a better landscape option.

For the owner who does want to harvest their olives, now is the perfect time to start taking precautionary measures to ward off the fruit fly. A coalition of neighbors acting against the fruit fly in the same area can provide the best line of protection.

Both Don Landis of ( and Sonoma Mission Gardens (851 Craig Ave., Sonoma, 938-5775) provide good resources for anyone with one tree or an entire orchard. In light of the increased numbers of flies being spotted in the valley, Sonoma Mission Gardens hosted a pest workshop last month and recently put out an Olive Fruit Fly Alert.

Olives certainly aren’t Sonoma County’s most popular crop in terms of acreage or value, but they are nonetheless a growing niche industry that has inspired events like the Sonoma Valley Olive Festival and destination olive oil tasting experiences.

This year’s crop yields won’t be tallied for another few months, but, just like in the vineyards across the county, buds are in bloom on the olive trees and what is done now will have ramifications for the future.

Sarah Phelps is an editor and reporter. She was raised in Kenwood and has a BA from Loyola Marymount University.

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