Growers, Gardeners: Be On Lookout For Significant Grape Pest

News from Napa County:

After an adult Western Grapeleaf Skeletonizer, was discovered in a vineyard trap June 24 on Tubbs Lane in Calistoga, Napa County Agricultural Commissioner Greg Clark is asking growers and gardeners to watch for all larval (caterpillar) stages of this injurious moth.

“This is a destructive and serious pest,” Clark said. “All larval life stages are voracious feeders that cause extensive damage to grape leaves, including partial or complete defoliation of grapevines. Excessive feeding can damage fruit and lead to secondary fungal damage and rot of grape clusters. We do not want this pest to become established in Napa County.”

The adult Western Grapeleaf Skeletonizer was found in a pheromone-baited trap, which can attract moths from as far as 1.5 miles away. Pest detection trappers in the Agricultural Commissioner’s Office are increasing trap density by deploying 25 additional traps within a mile radius of the Calistoga find.

Although the pest is not native to Napa County, it has been found here a number of times in the past, most recently on Mt. Veeder Road in 2007. Native to Arizona and New Mexico, it was first discovered in California in the 1940s and eventually spread throughout the state, particularly in the Central Valley.

Damage caused by the Western Grapeleaf Skeletonizer is relatively easy to detect. When it feeds on grapevines, it leaves only the veins, producing a very distinctive, lacy skeletal appearance. This pest may also be found on Boston ivy and Virginia creeper. The larval stage is distinguished by bands of color around the body.

For more information and photos, please visit the Napa County Agricultural Department’s Web site at http://www.countyofnapa.org/AgCommissioner/Pests/.

If you suspect you may have found a Western Grapeleaf Skeletonizer caterpillar or adult moth, please bring it in to our office or contact us to help identify it.

We are also asking our growers, vineyard managers, wineries, and residents, who may be transporting farm equipment or winegrapes into Napa County to inspect these items to ensure that they are free from Western Grapeleaf Skeletonizer or any winegrape pests.

“Thanks to the cooperation of the wine grape industry and the community, as well as a very effective pest detection trapping program, the Ag Commissioner’s Office has been successful in preventing this pest from becoming established,” Clark said.

For more information, please call the Agricultural Department at (707) 253-4357.