Cold winter, spraying may have cut spotted-wing drosophila numbers
By DAN WHEAT
WENATCHEE, Wash. -- In April, Washington State University entomologists doubled their traps for spotted-wing drosophila in central Washington cherry orchards, bracing for earlier and larger infestations this season.
So far, the dreaded pest is neither early nor in great numbers. That's good for cherry growers.
"In terms of weather, it's an overall late year and the spotted-wing drosophila seems to be following along," said Elizabeth Beers, entomologist at the Washington State University Tree Fruit Research and Extension Center in Wenatchee.
Increase of the bug at the end of last season was one reason Beers and others thought earlier this year it might be a bigger problem.
But as of July 29, spotted-wing drosophila had only been caught in five central Washington traps, two in commercial orchards and three in backyard stone fruit trees, including an apricot tree, Beers said.
The two commercial finds were in cherry orchards, including one in Orondo, a hot spot last year, she said.
Growers may be spraying more to combat them this season and the cool spring may have slowed their development, she said. Last year's pre-Thanksgiving Day sub-zero temperatures probably took a toll, she has said.
The highest count has been four flies in one trap. Last year by this time they were showing up on a regular basis, Beers said.
Numbers have been low so far in red raspberries in Western Washington but growers, fearing an outbreak, have been spraying, said Lynell Tanigoshi, WSU entomologist at Mt. Vernon.
Trap counts have been low, one to five flies per week, in commercial berry farms but higher, 15 to 20, in home gardens from Medford to the Willamette Valley, said Vaughn Walton, Oregon State University entomologist in Corvallis.
"We expect it increasing in the next week or so up the Willamette as blueberries ripen," he said. "It's controllable with pesticides."
Last year's central Washington count peaked at 2,200 flies in one trap in a cherry orchard near Royal City during the first week of November and a total of 6,539 flies in four traps. That was 40 times greater than the norm of all traps in Eastern Washington in October, which had been a heavy month.
Beers deployed 400 apple cider vinegar traps in cherry orchards throughout central Washington this spring, double the number of last season. WSU traps in winegrape and juice grape vineyards were increased from 160 to 200.
Beers expects an upswing in trap counts at the end of August.
"We assume trap numbers are a relative indicator of populations but we don't know the ratio," Beers said. "We have a lot to learn."