What's the strategy for SWD?
Washington growers want guidance on what to do about the new pest spotted wing drosophila.
A spotted wing drosophila larva on a cherry.
Elizabeth Beers, WSU
Now that the spotted wing drosophila has been found throughout Washington State, growers are wondering what is the best strategy for dealing with it.
Across the Columbia River in Oregon, where it was found during the 2009 season, there was a coordinated effort to monitor the new pest, led by Dr. Peter Shearer at Oregon State University’s Mid-Columbia Research and Extension Center in Hood River.
OSU Extension Educator Lynn Long in The Dalles issued weekly reports of trapping results starting with the first find in early May. Trapping continued through the season and after harvest in cherries as well as other hosts such as grapes and blackberries.
The pest was found over the Canadian border in British Columbia’s Okanagan Valley in the fall of 2009. The Okanagan Kootenay Cherry Growers Association collaborated with other fruit industry groups to obtain provincial and federal funding to tackle the pest.
The OKCGA funded a trapping program in 2010 with almost 350 traps that were monitored throughout the season by packing house horticulturists. Trap catch data and other information are available online at www.bccherry.com.
The B.C. cherry industry is taking the pest very seriously. The Okanagan Tree Fruit Cooperative does on-porch screening of cherries before accepting them for packing at its warehouse. This season, it had to reject some grower lots, reported Charlotte Leaming field horticulturist with the cooperative. The numbers of drosophila caught in traps increased as the cherry season progressed, as did the number intercepted in fruit samples. Leaming noted that when fruit is ripe, it can be more attractive to the insect than traps, so trap catches don’t necessarily reflect the magnitude of the populations.
In Washington, information about the pest was harder to come by, leaving growers feeling vulnerable.
Denny Hayden, a grower at Pasco, Washington, said Washington State University Extension faculty gave assurances they were monitoring the situation, but he was frustrated by the lack of information and the wait-and-see approach. He started trapping in his own orchard in the spring. “We knew there was a potential problem out there from the fall meetings last year,” he said.
Hayden attended a workshop on the pest held in Oregon in the spring, which explained how to identify the insect and trap it and coordinate efforts to control it. “They were organized early and communicated well, and had some go-to people.” He hoped there would be something similar for growers in Washington so they knew what to do and who to contact if or when the pest showed up.
Washington’s first fly was trapped by a private consultant in a Mattawa cherry orchard on June 28. That prompted an intensive trapping program, starting in early July, by industry horticulturists who checked about 240 traps throughout the state. WSU entomologist Dr. Elizabeth Beers and her lab examined the trap catches to identify the drosophila species. In late August, a summary of results showed that the pest was found throughout central Washington.
With the cherry season over and more drosophila showing up, growers were wondering what their strategy should be. What did the trap counts mean, Hayden wondered? How much benefit would postharvest sprays be?
“There are so many questions out there,” he said.
Dr. Jim McFerson, manager of the Washington Tree Fruit Research Commission, said very little is known about the pest, which is disquieting to growers.
“It’s a pest of considerable potential concern. It’s here and everywhere, no one knows about it and rumors abound, and there’s not a good source of science-based knowledge,” he said.
There’s been no point person for people to go to and information about the pest has not been issued in a coordinated fashion, he added. Complicating the issue is the fact that growers are reluctant to let people know if they find it.
“We haven’t had a response commensurate with the potential risk of this pest by research and Extension,” McFerson said. “I think it shows the lack of capacity we have in Extension. When it gets right down to it, the problem is just that. We really don’t have the capacity to deal with the problem as it ought to be dealt with. Frankly, I don’t see anyone stepping up at WSU to assume that leadership role.”
Dr. Mike Willett, vice president for scientific affairs at the Northwest Horticultural Council, said there’s been only limited information made available to Washington growers so far about the distribution and occurrence of the fly, and communication needs to be improved before the 2011 season to ensure that growers can adequately manage the pest.
Randy Baldree, WSU’s Extension director for agricultural programs, said Doug Walsh, WSU’s Statewide Integrated Pest Management advisor, is the state’s point person for the spotted wing drosophila and WSU provided resources to county Extension offices. “A lot of people were doing a lot of things trying to respond to local issues. We had a robust and conscientious effort going on statewide around the spotted wing drosophila.”
Dr. Dan Bernardo, dean of WSU’s College of Agricultural, Human, and Natural Resource Sciences, said that it may appear that OSU has taken more leadership on the issue, but the two universities are working together. “In this day and age, people are going to have to get used to receiving information from a variety of sources.”
Walsh told the Good Fruit Grower he does not recommend postharvest or areawide sprays because of the risk of disrupting IPM, but Hayden thinks growers would take a less conservative approach and would be willing to treat their orchards if they’re infested in an effort to get ahead of the pest.
In an October 1 e-mail, Tim Smith, WSU Extension educator for north Central Washington, said most potential tree fruit hosts had been harvested, but populations of the pest continued to increase on alternate hosts such as raspberries and blackberries. It had been reported infesting late-season cherries missed during harvest and ripening Bartlett pears that were dropped during harvest.
Smith said most entomologists agree that postharvest sprays in orchards that are infested or have high trap catches are not advisable. Beers said that they do not appear very effective and cold winter temperatures are likely to have a greater effect.
Leaming said that in late summer, a general recommendation was issued for B.C. growers to spray soft fruits, such as peaches, nectarines, prunes, and plums because of the high numbers trapped in cherries.
She is trying to promote sanitation as a way to tackle the pest because populations build up quickly on fruit left in the orchard after harvest. The pest is difficult to control with sprays because the larvae that develop inside the fruit are protected.
More research is needed, however, on how best to dispose of unharvested fruit in an economically feasible way, she said. For example, can cherries be dropped and mowed, or is it necessary to carry them out of the orchard?
Leaming said the B.C. industry plans to develop recommendations over the winter and announce a plan to growers early next year.