Glassy-winged Sharpshooter Nursery Subcommittee Update

by John Kabashima

On September 17, 2014 the Glassy-winged Sharpshooter (GWSS) Nursery Subcommittee met at the UC ANR South Coast Research and Extension Center in Irvine, California.  This subcommittee reports to the California Department of Food and Agriculture Pierce’s Disease Control Program (PDCP), which is funded from federal funds and industry assessments totaling over $18.3 million.

In the opening remarks the committee was informed that several Pierce’s Disease (PD) and GWSS research projects have made significant progress, including five GMO field trials and conventionally propagated grapevines that are providing resistance to PD. Reports were presented for the following programs:

Regulatory Nursery Program

There are 550 nurseries within the infested areas of the state under GWSS compliance agreements (fig. 1).  There were 30,575 shipments through July 31, 2014.  Shipments are down slightly in the regulatory program as compared to 2013.  Eleven Notices of Rejection (NORs) have been issued year to date.  Most areas are seeing an increase in pest pressure this season.  Year to date, origin county inspectors have stopped more than 176 egg masses, 4 nymphs, and 9 adults from moving in nursery stock shipments.

Fig. 1. Nursery stock in GWSS-infested areas must be inspected to ensure that this invasive pest isn’t moved in plant shipments. Photo: Matt Daugherty

Approved Treatment Protocol (ATP).There are eight nurseries that are participating in the ATP with 28 associated shipping yards.  This year, the total number of shipments through July 31, 2014 was 8,095, consisting of 1.46 million plants shipped to destination counties.  No viable life stages have been found in any ATP shipments.  Total number of shipments and plants shipped are up slightly from last year.  Six egg masses from four ATP yards have been sleeved by destination counties, with no GWSS emergences.  Ten out of 28 yards had holds due to trap finds with >10 GWSS adults.  There has been an increase in the number of GWSS trapped this year compared to last year.  ATP nursery holds tend to peak in July.   This can be attributed to a variety of factors, including the GWSS lifecycle and activity in the citrus and avocado nearby.  From July to August, there was a reduction in pest pressure.  The PDCP conducts quality control at each ATP nursery by placing water sensitive paper on plants staged for treatment to monitor the coverage.  Year to date, 205 papers have been placed and only 7 indicated the need for partial retreatment of the shipment. The Monterey County Agricultural Commissioner’s Office continues to do residue sampling from ATP nurseries and the results have indicated good coverage this year.  Napa County’s residue samples have also been very good.

The agricultural commissioners’ workload is much better now with the protocol adjustments that have already been made.  It was suggested that the Subcommittee look at eliminating the hold period as a result of trap finds with >10 GWSS adults.  The hold would still apply until the hold treatment occurred.  It was decided that the PDCP would draft up the proposed change and consult with the California Agricultural Commissioners and Sealers Association (CACASA) GWSS Advisory Group.  The outcome of that discussion will be shared with the Subcommittee. 

Applied Research

Two research projects have been funded by the PD/GWSS Board exploring insecticide resistance in GWSS populations in California.  One study, headed by Dr. Thomas Perring, UC Riverside, is a two-year project that will focus on Central Valley GWSS populations and is 50% funded by the Consolidated Central Valley Table Grape Pest and Disease Control District.  Dr. Perring’s study began on July 1, 2014.  The second study — headed by UC Riverside’s Dr. Rick Redak, Dr. Frank Byrne and Dr. Bradley White — will also explore the Central Valley resistance concerns and additionally has a broadened scope to include populations from agricultural, nursery and urban settings.  This project is funded for a three-year period, and began July 1, 2104.

Rapid Response

Fresno County has continued suppression treatments in 2014 in and around the Fresno/Clovis and Kingsburg areas.  Year to date, over 3,600 properties have been treated in urban and rural areas. In Santa Clara County, there is one remaining infested area in the county, the Capitol area of San Jose. In response to a late season find in 2013, about 76 properties were treated in March 2014.  The first Capitol find of 2014 was in an apartment complex and the county, coordinating with the apartment management’s pest control operator, scheduled treatments in and around the find site.  In Tulare County, there have been GWSS finds in the Visalia area, which is outside of the existing infested area.  The county is still delimiting the area and treatments have just started in response to the finds.  The exact size of the area is still to be determined.  There have been a handful of nursery trap finds in the non-infested areas of the state that have not indicated any breeding GWSS populations and appear to be isolated finds.

Area-Wide Program

The area-wide suppression treatments mainly target citrus, a preferred over-wintering host of GWSS.  In the Temecula Valley area of Riverside County there is no longer funding for treatments; however, a trapping program is in place to monitor the GWSS populations.  Year to date, 617 GWSS have been trapped in Temecula. Three GWSS have been trapped year to date in the Coachella Valley of Riverside County.  In Fresno County, there have been some area-wide finds further west than seen before, with a total of 36 GWSS trapped year to date.  Madera County has not had any GWSS detections this year.  In Tulare County, there have been 2,598 GWSS trapped year to date, although 80% of those finds come from one organic ranch.  Organic groves continue to be a challenge as there are not highly efficacious organic chemicals available.  Fall foliar treatments are being scheduled for Tulare County.  In Kern County, there are several zones trapped for GWSS.  Year to date, there have been significant treatments made, mainly in the General Beale area, to control GWSS.  Windbreaks continue to present a challenge in Kern County due to the fact that they serve as a reservoir for GWSS and insecticide coverage is difficult due to their size.

John Kabashima is Environmental Horticulture Advisor, UC Cooperative Extension Orange County. The information used in this article was provided by the CDFA.