Voracious vineyard pest ‘skeletonizer’ moth detected in Napa County

Katy St. Clair | Bay City News Foundation

Authorities in Napa County are sounding the alarm about a moth known to cause “significant” damage to grapevines after an insect trapper discovered it earlier this month and reported it to the county’s agricultural commissioner.

The moth, dubbed with the rather heavy metal name “Western grape leaf skeletonizer” is from the species Harissina metallica and is described by the county as a “voracious feeder” that can cause extensive damage to grape leaves, often resulting in partial or complete defoliation of grapevines. The feeding can also damage fruit and lead to secondary fungal damage.

“We do not want this pest to become established in Napa County,” stated Tracy Cleveland, county agricultural commissioner.

The insect trapper, Jesse Guidi, had been monitoring the presence of another pest in Pope Valley, the glassy-winged sharpshooter, when he encountered the skeletonizer on May 12.

The commissioner has ordered that 25 additional traps be employed within a mile radius of Guidi’s discovery.

According to the county, the skeletonizer is not native to the area and was last seen in the Napa region in 2018. The pest first arrived in California from Arizona or New Mexico in the 1940s.

Authorities say evidence of the moth’s presence is fairly easy to spot, as it leaves only a leaf’s veins behind, producing a distinctively lacy appearance.

The skeletonizer also likes Boston Ivy and Virginia Creeper. In its larval stage, it displays colored bands around its body.

Cleveland is asking Napa County residents that suspect they have found a Western grape leaf skeletonizer caterpillar or adult moth to bring it to the county office “immediately” or contact them in order to help identify it.

Growers, vineyard managers, wineries and residents are asked to inspect any farm equipment being transported into the county to ensure that they are free of the pest, as well.

The Napa County Agricultural Commissioner’s Office can be reached at (707) 253-4357.