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PNW scientists keep an eye on grape leaffolder

David James/WSU GL0812-WSU-leaffolder.jpg
White-headed grape leaffolder larvae fold leaves over to protect themselves from predators.
There’s ‘a lot of unpredictability’ in the pest, expert says.

On a scale of 1 to 10, Washington State University entomologist David James calls the recent discovery of the white-headed grape leaffolder about a 5 on the reason-to-be-concerned meter.

“There’s a lot of unpredictability here,” he said. “Normally when there’s a new pest on the block, it’s going to be a big problem because it envelopes the whole region, but this one is localized and has stayed put.  I don’t see it as being an industry-wide problem — but I could be wrong.  That said, it’s a significant problem for the people who already have it.”

Speaking at a WAVEx webinar co-sponsored by the Washington State Wine Commission and Washington State University, James said the caterpillar/moth pest was discovered a few years back in specific vineyards in the Columbia and Yakima Valleys with near-defoliation of some young vineyards.

Usually when a new pest appears in a spot location, it eventually begins to spread.  “Normally it will and it’s very unusual for something like this that has wings and is fairly mobile that is hasn’t popped up in other locations,” he said.  “That’s a bit of a mystery as to why it’s not apparently dispersive.  Insects have a reputation of just suddenly becoming dispersed and I can’t say categorically it’s never going to be a problem.  Right now, it’s still a relatively small problem.

James has been studying the pest for three years now, trying to learn more about the lifecycle, economic impact of the insect, and potential control methods.  “We know a lot more now about its biology and its generational history although much remains a mystery still,” he said.  “We continue to monitor with simple date traps to keep tabs on population sizes as their numbers increase towards the end of the season when more damage appears.  We want to make sure whatever control methods we implement are not going to disrupt the rest of our IPM system.  We have a great grape IPM system here in Washington and the last thing you’d want to do is mess that up.”

Folded leaves observed

The pest problem arose when growers in specific vineyards in South Central Washington noticed folded leaves in their crop caused by feeding caterpillars.  Initially it was assumed to be the California variety of leaffolder, but it turned out to be a closely-related species.  “It’s probably been there for a while, just never documented until the economic damage began,” James said.

“Caterpillar larvae evolve and develop through a number of stages and as they get larger, they fold leaves over to protect themselves from predators, literally forming a little envelope to hide in.”

With research still on-going, “We don’t exactly know what their real impact will be and growers, to this point, don’t consider in most cases, there’s been any severe economic damage with little indication of fruit contamination. We still know very little about its biology, ecology, or distribution, primarily because it’s so similar to other species, it most likely hasn’t been recognized as distinctive in a lot of instances.”

Asked what might happen if the California species and the Washington species decided to meet for a family reunion, he responded: “They’re so very closely related and could well integrate, so that’s not such a crazy idea.  But for now, there’s no reason to panic as the pest is not regionally explosive --- like stinkbugs or lanternflies.  It doesn’t occupy a huge geographic area at the moment, allowing us time to work on being better prepared if it does become more widespread.”

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