Yet another reason for a Pest Control District

Subject: Invasive pest found in Napa County

The following information will be announced by the County Public Information Officer on May 20. 

On May 12, 2022, a county pest detection trapper discovered a single adult Western Grapeleaf Skeletonizer (Harrisina metallica) in a trap located in Pope Valley near Dollarhide Road.  The Western Grapeleaf Skeletonizer (WGLS) is a significant and destructive winegrape pest not known to be established in Napa County. All larval life stages are ravenous feeders that cause extensive leaf damage, including partial or complete defoliation of grapevines, especially on young vines. Excessive and uncontrolled feeding can damage fruit and lead to secondary fungal damage and rot of winegrape clusters.

Agricultural Commissioner staff have been in contact with the property operator to discuss the find and they are taking steps to respond to this issue.  Our department has responded to the WGLS find by placing 25 additional WGLS traps within a one-mile radius of the find and have requested all growers with vineyard property within this one-mile radius to be vigilant while inspecting their vineyards.

As this pest is rated as a “C” pest, there is no state enforcement action.  Additional finds of this pest may warrant further action on the part of the Agricultural Commissioner; however, delimitation trapping will continue throughout the remainder of the growing season and additional traps will be placed within the one-mile radius next year as well. WGLS was last detected in Napa County in June 2018 in Calistoga near Tubbs Lane, delimitation trapping was conducted with no further finds of the pest in the area.

The Napa County Agricultural Commissioner’s Office request that growers, wineries, and residents become familiar with the pest’s appearance and feed behavior (refer to attached flier), similarly train employees, and contact our office at (707) 253-4357 or email Agcommissioner@countyofnapa.org if you think you have found WGLS.

WGLS may also be found or cause feeding damage on wild grapes, backyard grapes, Boston ivy (Parthenocissus tricuspidate) and Virginia creeper (Parthenocissus quinquefolia). Please be sure to also examine any of these plants if you have them on your property.