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New pest discovery in Washington grapes

David James/Washington State University GL0527-WSU-pest.JPG
An adult leafminer moth.
Leafminers found last fall in two commercial vineyards.

For growers, it’s a constant search through their vines for new faces that may have joined the world of pests.

Entomologists in Washington State found one last year and researcher David James at WSU said: “We know very little about it at this point. There are hundreds of different species of leafminers for different crops, but for grapes, this one doesn’t even have a name yet. We know its genus, but it’s still an undescribed species. We’re hoping to learn more this year as the vines enter their new season.”

Found last fall at the end of the season at two commercial vineyards, the levels of discovery were insignificant and no further surveying was done. 

“It could be a lot more widespread, so that’s the priority this year is to see how extensive its distribution is in Eastern Washington vineyards,” James said.

Leafminers are insects that feed within a leaf, producing large blotches or meandering tunnels as they feed for their entire larval period. Although the areas mined by leafmining insects tend to dry out and die, there is general concurrence that although these produced injuries can be unattractive from an esthetic viewpoint, it is rare for them to significantly affect a plant’s health.

“This isn’t a truly destructive pest, but a secondary one, although this discovered species is in the same genus as the citrus leafminer and could become an issue most likely in nursery grapes where growth could be curtailed or restricted,” James said.

“The citrus leafminer has been known to introduce disease organisms into the plant itself and although we don’t anticipate this will become a serious issue for Washington grapes, it could be a minor annoyance in the form of a cosmetic issue as they scribble across the leaf leaving travel lines.  With luck, those travel routes could be the end of it.”

Disease potential

However, any time an insect carves a path through a part of a plant, it opens up opportunities as a potential disease conduit.

“That’s true with the citrus leafminer that has been implicated as a cause for those sorts of problems,” he said. “It’s an issue with that species, so it might be a potential problem, but we can’t be one hundred percent sure of anything at this point.

“It’s unlikely to become the new big pest issue in Eastern Washington grapes although the industry has funded this year’s survey because they consider it worthy of further investigation to be sure it isn’t going to be anything more than a cosmetic concern,” he said. “At this time next year, we should know a whole lot more about this latest discovery.”

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