WENATCHEE, Wash. — Spotted Wing Drosophila, now in its ninth year of being tracked in Central Washington, no longer is the huge worry it once was, but scientists continue to combat it, Little Cherry Disease and other sweet cherry ailments.
SWD is an Asian pest first detected in the U.S. in California strawberries in 2008. It moved into berries in Oregon’s Willamette Valley and into Central Washington cherries in 2010.
The initial fear was it could devastate cherries. Scientists didn’t know how severe it might become.
“We’re learning to live with it. We have no choice. We’ve come a long way. We have better knowledge of its biology, distribution and management and we’re not as alarmed as we once were. It’s more familiar,” says Elizabeth Beers, Washington State University entomologist in Wenatchee and lead scientist on the pest’s case in Washington since 2010.
A total of 44 SWD were found in Central Washington cherry packing houses in 2013, nearly none in 2014, around 250 in 2015, about 30 in 2016 and eight in 2017, Beers said. A mild winter likely contributed to the 2015 spike, she said.
It is contained with moderately broad spectrum pesticides when cherries turn from green to yellow and until harvest.
SWD was down in 2017 and Cherry Fruit Fly was up a little, she said. CFF is less prevalent. Growers keep tight control on it because it results in quarantine.
Little Cherry Disease was a big problem many decades ago and has increased since or before 2009 with Wenatchee as the hot spot.
The incurable pathogen comes in three strains, robs trees of energy, reduces production and results in small fruit that’s unmarketable.
Little Cherry Virus 1 and 2 take away fruit flavor and the Western X Phytoplasma strain leaves bitter-tasting fruit. The pathogen overwinters in roots and spreads tree-to-tree in roots. Apple and grape mealybugs spread virus 2 which is about 60 percent of LCD and 2016 studies show leafhoppers carry Western X.
Bugs can be sprayed but the best combat is removing infected trees and trees close around them and not replanting for while, scientists say. The disease spreads slowly.
More than 1,000 acres of cherry orchards in the Wenatchee area have been removed because of the disease in the past several years. Orchards have been removed in Orondo, Mattawa and Benton City.
There was a general increase of LCD in 2017, said Scott Harper, WSU plant pathologist in Prosser.
Harper is developing real time Polymerase Chain Reaction testing, more sensitive to lower amounts of infection in leaves and tree tissue, to detect the disease before symptoms show so that trees can be removed earlier and reduce chance of spread.
Western X has been showing up in young cherry trees with no known infestations nearby to have spread from, Harper said. So another project is trying to determine how that happens, if it’s coming from unknown hosts.
LCD runs 10 to 30 percent infection rates which is high enough to be a concern, Harper said.
Cherry Rasp Leaf Virus is increasing but probably less than 5 percent, so not alarming, he said. Cherry Leafroll Virus, Prune Dwarf Virus and Prunus Necrotic Ringspot Virus have been around a long time and continue at low levels, he said.