24 Oct

olive fruit fly: New hope for home gardeners

By Holly Hayes

For generations, many gardeners in California were accustomed to growing olives for oil or table fruit. Then came the invasion of the olive fruit fly, which was first discovered in the Los Angeles area in 1998 and quickly spread throughout the state’s olive-growing regions.

Commercial growers fairly quickly had tools to control the pest. But until recently, the only advice for home gardeners was tough to hear, especially for longtime hobbyist olive processors: Dispose of the fruit in plastic bags and put it in the garbage.

Now an organic insecticide-bait with the active ingredient spinosad – GF-120 NF Naturalyte made by Dow AgroSciences – is available to non-commercial growers. The adult flies are attracted to the bait, feed on it and die.

“The problem is finding it, and it’s expensive,” says Michelle Thom, a biologist with the Santa Clara County Division of Agriculture. One local source is Sierra Pacific Turf Supply, 510 Salmar Ave., Campbell (408-374-4700), where the concentrate costs $110 a gallon – when they have it in stock.

And if you’re going to spray, timing is critical, Thom says. “You need to get familiar with the life cycle of the pest,” she says, noting that there are two generations a year – one in spring and another in summer. Spraying when the insect is not present is a waste of time and the product.

Another organic treatment is kaolin clay (brand names include Surround WP and Surround at Home), which acts as a repellent rather than an insecticide. The downside of the clay treatment is that it dries to a white powder, which makes the trees look ghostly – not a great side-effect for an ornamental tree.

Trapping by various methods also has shown promise.
To help stop the spread of olive fruit fly – which reproduces only in olives – state officials suggest that gardeners who grow olive trees strictly for ornamental reasons should plant fruitless varieties such as “Swan Hill,” “Majestic Beauty,” “Wilsoni” and “Little Ollie.”

Gardeners who have no intention of harvesting their olives are urged to spray with a product such as Florel or Fruit Stop to prevent fruit set.

Santa Clara County has a helpful page on the olive fruit fly at www.sccagriculture.org (click on “insect pest ID and management”). Also, check out “A Homeowner’s Guide to the Olive Fruit Fly” at www.oliveoilsource.com and “Controlling the Olive Fruit Fly at Home,” which can be found by going to cesantaclara.ucdavis.edu and typing “olive fruit fly” into the search field.

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