Orchardist Stuart Olson is among Oregon farmers, state regulators and entomologists that today have a heightened awareness of a tiny fly with a wide host range that feeds on fresh fruit.

SALEM — Orchardist Stuart Olson a few weeks back was struck with the sudden appearance of what he thought was brown rot on his peaches.

The late-maturing Elbertas were clean just days before the sudden arrival of the rot and there was no indication rot was developing.

Olson put two and two together, started doing some research and before long realized it wasn't a rot. His peaches were being invaded by a pest new to the Willamette Valley.

Olson is among Oregon farmers, state regulators and entomologists that today have a heightened awareness of a tiny fly with a wide host range that feeds on fresh fruit.

Contrast that from a month ago, and most Northwest farmers and regulators had never heard of the spotted wing Drosophila suzukii.

Today, some fear the vinegar fly could emerge as one of the worst insect pests to invade the valley and potentially the entire Northwest in years.

"It couldn't come at a worst time for agriculture," Olson said. "With commodity prices where they are and this insect coming along, it has the potential to be very serious for agriculture in the state of Oregon."

Among reasons Olson is concerned, the pest is highly adapted to Oregon's temperate climate; has a host range than includes wild blackberries; multiplies rapidly; and unlike fruit flies that feed on rotten fruit, the vinegar fly feeds on ripe and ripening fruit.

"Frankly, we think it is potentially a big deal," said Jim Cramer, administrator of the Oregon Department of Agriculture commodity inspection division. "And from a management perspective for these growers, it definitely is a big deal."

Olson fears that unless scientists and growers can devise a way to control the pest at a reasonable cost, come next spring, when fruit starts ripening, growers could have an immense problem.

"It's a harmless looking little insect," Olson said. "But the economics of this thing could be millions and millions of dollars."

The Drosophila suzukii has been present in Japan for decades, but only in the last couple of months has it emerged as a pest of concern in the United States. Today it is found in California, Oregon, Washington, British Columbia and Florida.

In Oregon, the pest reportedly has not been found in orchards in Hood River or The Dalles but has been reported throughout the Willamette Valley.

Olson's main concern is the potential for the pest to dramatically increase his pest control cost and disrupt his existing integrated pest management program.

Females lay up to 400 eggs per life cycle, according to Helmuth Rogg, an entomologist with the Oregon Department of Agriculture, and the pest is known to have as many as 13 generations per year in Japan.

Olson said the pest went from a minor presence to an infestation in a matter of days on his farm. In three or four weeks, Olson said, the pest destroyed 20 percent of his Elberta peaches in a 3 acre orchard.

With blackberries growing wild outside his orchard, and with Olson growing a variety of crops on his U-pick farm, even good control practices might not be effective, he said.

Rogg agreed the pest could be extremely difficult to control.

"We are concerned because we have lots of feral fruit like the Himalayan blackberry, so they can multiply around an orchard and infest an orchard from the feral fruit," Rogg said.

To date, state officials, entomologists and farmers have far more questions than answers, Rogg said.

"We're working with OSU (Oregon State University), the USDA Agricultural Research Service in Corvallis and we're researching literature and checking with other countries to see if we can do something about it," Rogg said.

The only good news, Cramer said, is at this point, most of Oregon's 2009 fruit crop has been harvested, packed and shipped.