Spotted wing drosophila makes early appearance
Pest is showing in traps in more areas than last year
By MITCH LIES
For the first time since the spotted wing drosophila arrived in the Northwest three years ago, the fly appears to be a threat to strawberries and cherries.
Fly numbers are building in Oregon's Willamette Valley much earlier than scientists anticipated.
"This year, earlier crops such as strawberries, and potentially cherries, will be more susceptible than they were the last two years," said Vaughn Walton, an Oregon State University Extension entomologist in Corvallis.
Vaughn attributed the early fly development to a relatively mild winter that led to strong winter survival and early hatch.
Cold winters and cold, rainy spring weather the last two growing seasons delayed fly development, he said, and spared early-maturing fruit.
"We had a milder winter, so we anticipated there would be more of an overwintering population, and that is what the traps are showing," said Tom Peerbolt of Peerbolt Crop Management.
Peerbolt said fly counts in one cherry orchard went from 9 one week to more than 1,000 a week later.
Researchers are catching large numbers of flies in Willamette Valley sites where fly populations were low in previous years, Walton said.
Researchers in Washington also are reporting significant fly catches, said Peter Shearer, a Hood River County extension entomologist.
"They already have caught flies in five districts," Shearer said. "They didn't see that until the middle of August last year."
Minimal numbers are being trapped in the mid-Columbia region, Shearer said, but at more places than last year.
The scientists are advising growers to watch regional trap counts and do their own trapping.
"Trap in fields and surrounding vegetation," Walton said.
Also monitor fruit development, Walton said. The riper the fruit, the higher its susceptibility.
Shearer estimated early cherries in the mid-Columbia region would be nearing straw color by June 1, at which point they will be susceptible to fly damage.
The spotted wing drosophila scars fruit by depositing eggs in it with a saw-like ovipositor. The scar allows secondary organisms such as botrytis into fruit, which can lead to rotting.
Soft skin fruits, such as strawberries, cherries, blackberries and raspberries, are particularly susceptible.
The pest is native to Asia.
Growers can obtain up-to-date information on the pest from a newsletter OSU is publishing through the growing season.
The first four are available in printed form. All nine newsletters are posted on OSU's spotted wing drosophila website, swd.hort.oregonstate.edu .
The first two updates were on strawberries on May 4 and blackberries on May 20.