Grapeleaf skeletonizer

This is an image of the adult western grapeleaf skeletonizer, which devours the leaves on grapevines. One adult moth was found in June in a vineyard near Calistoga, prompting expanded efforts to find more.

University of California photo

A leaf-consuming grapevine pest with a Halloween-like name apparently ended up being only a brief visitor to Napa Valley this summer.

A single western grapeleaf skeletonizer moth showed up in a vineyard sticky trap along Tubbs Lane near Calistoga in June. But further trapping has yielded no more of this invasive species.

“Good news,” county Agricultural Commissioner Greg Clark said.

The skeletonizer has caterpillars that devour leaves, leaving behind the veins and creating a kind of leaf skeleton. Less leaves let in more sun that can sunburn the fruit. The caterpillars can also feed on grape clusters and cause bunch rot.

Caterpillars have been known to defoliate entire vineyards in other parts of the state.

“This is a very serious pest,” Jennifer Putnam of Napa Valley Grapegrowers said after the discovery.

Napa County responded to the Tubbs Lane find by putting out 25 additional traps within a 1-mile radius.

Perhaps the lone moth hitchhiked to the area on farm equipment, Clark said. There doesn’t appear to be an infestation because the traps likely would have picked up additional moths.

Still, the county will continue to monitor the area for three years.

“We want to be vigilant,” Clark said. “We never know when a pest is going to be introduced, one that is significant and harmful to the environment, wine grapes and our economy.”

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In 2007, the county discovered a grapeleaf skeletonizer moth in the Mount Veeder area west of the city of Napa. That appeared to be a fluke, too, with no other moth turning up.

The grapeleaf skeletonizer is a native of Arizona, New Mexico and Mexico and was discovered in California in 1941. It is established in parts of the Central Valley. Unlike the glassy-winged sharpshooter or European grapevine moth, an infestation of grapeleaf skeletonizers doesn’t trigger a state quarantine.

Nor does the skeletonizer have the grape industry doomsday reputation of the glassy-winged sharpshooter, which spreads vine-killing Pierce’s disease.

“It is a destructive pest,” Clark said. “It is relatively easy to control using a variety of materials.”

But that costs grapegrowers more money. Napa County has the grapeleaf skeletonizer on its list of unwelcomed insects.

“For those of us who don’t have it and don’t want it, if we trap and find it early, the ability to eradicate is certainly a viable option,” Clark said.


Napa County Reporter

Barry Eberling covers Napa County government, transportation, the environment and general assignments. He was worked for the Napa Valley Register since fall 2014 and previously worked 27 years for the Daily Republic of Fairfield. He is a graduate of UC Sa

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