Wireworms in Western Washington
Christine Langley has successfully run Lopez Harvest, an organically managed farm on Lopez Island in Washington state’s famed San Juan Islands, for more than two decades. But for most of that, she wasn’t fighting wireworms.
Those showed up about a dozen years ago.
“I have other disease problems and insects, but they crop up here and there and you can control them,” Langley said. “Wireworms affect everything. When I talk to my farmer friends, it’s the first thing we talk about. ‘How are your wireworms? Oh, ours are fine.’ But I’m not fine with them being fine.”
And here's how bad fine can be.
“I grow a lot of lettuce for the restaurants and grocery stores here,” she said. “I would plant 100 feet of lettuce and maybe 40 percent of them would die. That’s not really acceptable when you’re trying to make a living.”
For years, Langley has been working around the wireworms – the larval form of click beetles that spend several years in the soil before emerging as adults.
“I noticed that it was worse in certain places in the field, so I’d plant things other than lettuce and potatoes in those areas,” she said. “I also found it was more problematic for me in late summer, so I would make sure that my least wireworm-infested rows were available then.”
Langley has also been growing and plowing under mustard crops as one way to reduce the wireworms in her vegetable plots. To give herself more options and space, she recently opened up a new field by converting a section of pasture.
“I thought I was solving the problem by opening some new ground,” she said. But wireworms love pasture, and Langley’s new field was even more infested.
“Wireworms prefer sod and certain grain crops,” explained Brook Brouwer, the director of Washington State University Extension in San Juan County, which encompasses all the islands. “As vegetable and market farmers move into those pastures, they’re tilling up that ground and you can have a really robust population of wireworms living in that soil. They’re hungry, and if you plant a crop it can be wiped out.”
So with a three-year grant from Western Sustainable Agriculture Research and Education program, Brouwer is looking for ways vegetable growers can mitigate wireworm problems. He’s testing planting a trap crop of wheat, both with and without an organic spinosad pesticide bait product.
“There’s really very little that will kill wireworms, so our approach is looking at damage mitigation,” Brouwer said. “If we can find a way to reduce the immediate damage they do, especially in new fields, in the long term we can begin to reduce their population.”
Some strategies that have been promoted to control the pests are intensive cultivation and bare-ground fallowing – cultural practices Langley is loath to do.
“Those things are so counterintuitive to me as an organic farmer that I’m hoping that’s not the solution,” she said. “I’m hoping there are other ways to approach this problem.”
So she’s curiously watching the trap-crop trials Brouwer has in her new field. In those, a strip of wheat is intercropped between rows of lettuce transplants, giving the wireworms a more-familiar food source.
“If it works, I’d do it for sure,” she said of the wheat. “One of the side benefits to me with both the mustard production and the wheat would be that it’s good organic matter for the soil. I’m an organic farmer and we’re all about organic matter. But I also realize organic matter is what the wireworms are attracted to.”