USDA GWSS Area-Wide Control Program
Once it was determined that the glassy-winged sharpshooter (GWSS) had established itself in California, the USDA established the area-wide control program in several Southern California regions. This program has become an important part of the overall efforts to limit the spread of GWSS and the Pierce’s disease (PD) that it spreads.
Beth Stone-Smith, the USDA APHIS GWSS Program Director headquartered in Sacramento, Calif., is in charge of the various area-wide programs located in Fresno, Madera, Tulare and Kern counties.
Here are some of the questions that are often asked about the program:
Q) What is the purpose of the area-wide control program?
It’s really multi-pronged, depending on what area-wide program we’re talking about. The overall purpose is to suppress GWSS populations in order to reduce the incidence of Pierce’s disease and the movement of this key vector. In an area like Tulare County, we are decreasing the chance of the natural spread of GWSS northward into un-infested areas. An added benefit for citrus growers who ship bulk citrus is that the area-wide program can aid them in complying with the state regulation of shipping bulk citrus GWSS-free (artificial spread).
Q) How does keeping the numbers low in infested areas prevent the spread of GWSS or PD?
Keeping population levels of GWSS low in infested areas means there is less chance of natural and/or artificial spread of the pest to areas either un-infested or areas under active control.
Research conducted by a UC Extension viticulturist in Kern County has proven that reducing the number of GWSS will also reduce the incidence of PD in vineyards.
Q) Has information/procedures learned or developed in the GWSS area-wide control program been applied to other ag commodities?
Yes. One example is the aphid treatment program for Tristeza virus going on at UC’s Lindcove Research and Extension Center Field Station. The Citrus Research Board’s Technical Working Group for Asian Citrus Psyllid (ACP) is bringing area-wide management practices learned in GWSS area-wide control program to the table for managing ACP. Click here for more info
In Texas they are doing some area-wide treatments for ACP, and USDA is involved with that as well, bringing in some of the same scientists from USDA that first came to Kern County and Temecula when GWSS area-wide programs started several years ago.
Q) Why isn’t there a program to just eradicate GWSS from the entire state?
The short answer is, too much area is infested. Then there are also too many hosts to chemically treat across such a huge area. Different host plants may require different treatments and frequency of treatments. There is no one treatment that works on all host plants all the time. The combination means eradication would cost too much and it’s just not feasible.
For instance, in a county like Los Angeles, it wouldn’t be feasible to attempt eradication because of the number of hosts that would need to be chemically treated (think about every home’s back yard in L.A. County and how many hosts are there for GWSS). It would be enormous and the costs associated with that would be even more enormous, not to mention how the public would feel about adding so much chemical input into a wide-scale eradication effort like that.
Q) What would happen if the area-wide control program were to stop this year?
If the area-wide control program were to stop, for grape growers it would mean that: local grape growers in infested areas would feel the impact first, with a greater risk of PD incidence due to vector populations increasing.
Over time, grape growers who are not currently impacted by GWSS would be impacted as there would be a greater likelihood of the natural and artificial spread of GWSS without a comprehensive area-wide program. GWSS would creep its way northward up the San Joaquin Valley (natural spread), and bulk citrus would become an increasingly high risk commodity to ship (artificial spread) with larger GWSS populations to keep in check.
Without a coordinated treatment effort, citrus growers would still have to comply with the state regulation to ship their bulk citrus GWSS-free. But what we’d see is a patchwork of treatments as growers only treat in order to move THEIR bulk citrus at that moment in time, leaving reservoirs of GWSS in other citrus orchards to survive and multiply. GWSS populations are not successfully suppressed with a patchwork treatment scenario. They are strong fliers and can easily move back and forth to areas that aren’t treated.
Without an area-wide program, we would see GWSS population levels get back to what we saw in the beginning of our program, hundreds of GWSS per trap per week. At times there were so many GWSS that sticky traps were full before they could even be changed out on the weekly schedule. When I started on this program in 2001, in Kern County you could walk out into a citrus orchard and GWSS were everywhere. In 2001 there were over 147,000 GWSS trapped in the General Beale Project area alone – that’s a 13,000 acre area of multiple commodities, 3,600 acres of that being citrus. By effectively treating that 3,600 acres of citrus (and some windbreaks), populations were dropped to near undetectable. We went from hundreds per trap per week to zero per trap per week.
What has been the overall cost of the area-wide control program?
That depends on the year. These are the number for only the treatments and does not include trapping activities that support the treatment decisions:
• 2001 = $1.25 million
(General Beale Area in Kern County & Temecula)
• 2002 = $2.37 million
(Additional areas in Kern County added to program,
Ventura County added)
• 2003 = $8.82 million
(Additional areas in Kern County added to program,
more widespread treatments added in Ventura,
Tulare County added, Coachella added)
• 2004 = $3.36 million
• 2005 = $2.21 million
• 2006 = $4.99 million
• 2007 = $2.47 million
• 2008 = $1.17 million
One thing to keep in mind as well is that chemical (imidacloprid) prices have dropped DRAMATICALLY since the beginning of the program. When imidacloprid went off patent in late 2005, we started seeing generics on the market, and that dropped prices.
Area-wide chemical treatment costs are funded by federal funds. In area-wide program counties the USDA has direct contracts with those counties for treatment funds. Area-wide trapping (the cost of traps/poles/personnel/vehicles/etc.) are paid for by state money.