Traps signal pest rebound

Ravenous insect munches on cherries; trap counts highest south of Interstate 90

By DAN WHEAT

Capital Press

WENATCHEE, Wash. -- Spotted wing drosophila, that dreaded Asian fruit pest, made a comeback in Central Washington in 2012 after laying low in 2011.

The season isn't over, so the numbers are not final, but 50,256 spotted wing drosophilas were trapped in Central Washington season-to-date through Oct. 26 versus 13,807 for all of 2011 and 60,381 in 2010.

The 2011 season was down because the pest was reduced by the pre-Thanksgiving Day freeze of 2010 and a spring freeze in 2011, said Elizabeth Beers, entomologist at the Washington State University Tree Fruit Research and Extension Center in Wenatchee.

"So we're looking at 2011 as the anomaly and 2010 and 2012 as the norm," she said.

She expects the final 2012 number to be close to the 2010 number even though there were fewer traps out this year because of less funding. There were 334 traps this year versus 593 in 2011 and 456 in 2010. The program was aided by half a dozen chemical distributors volunteering their fieldmen to run traps, Beers said.

Trap counts were highest south of Interstate 90 in the Mattawa and Tri-Cities areas. They were previously greatest north of I-90 around Quincy, Wenatchee, Orondo and Tonasket.

Beers said she expects it to do better in the warmer, southern part of the state.

Spotted wing drosophila was first detected in the U.S. in California strawberries in 2008. It damaged cherries and strawberries there and in the next year damaged berries in Western Oregon and Western Washington. It was discovered in Eastern Washington in 2010.

It is alarming because it attacks numerous ripening fruits and berries, not just damaged and decaying fruit, and has up to 13 generations per year.

The biggest threat in Central Washington has been to cherry growers. The spotted wing drosophila doesn't seem to like the acidity of grapes or the thick skin of pears and apples.

Cherry growers south of I-90 saw the most damage this year, Beers said. But she doesn't have an exact handle on numbers of growers and the severity.

"My guess is no growers were wiped out. Sometimes it was the later cultivars in a block that had problems," she said.

Spotted wing drosophila was detected for the first time in packed cherries by state Department of Agriculture inspectors this year, she said. There were 16 finds in packing houses.

The seasonal pattern has been the same each year -- few catches early and low trap numbers in summer, escalating in mid-August and peaking in October and November.

Noting weather is a big variable with all insects, Beers expects continued control with the use of spinosyns, organophosphates and pyrethroids since the softer GF-120 natural food odor bait for cherry fruit fly doesn't work on spotted wing drosophila.

Andy Kahn, a Wenatchee entomologist consultant, said spotted wing drosophila appears manageable as long as growers pay attention to the WSU regional trap count updated daily during cherry growing season. Spraying when there are catches and when fruit is ripening is critical, he said.