Agencies Issue Grape Moth Advice

California wine industry's quarantine details released in effort against European pest

by Paul Franson
European Grapevine Moth
Google Earth image shows California areas already under quarantine for European Grape Moth infestations.
Napa, Calif. -- The International Technical Working Group for the European Grape Vine Moth (EGVM) in California issued its second and final report after meeting in Napa recently. It includes specific recommendations for controlling the invasive pest in Napa County, but the recommendations apply to the other seven infested counties in California, too.

Control will involve considerable effort by growers and wineries and grape transportation companies. The working group identified the EGVM as the cause of severe damage late last summer in several vineyards in Napa County, where the insects and associated Botrytis infections caused complete loss of harvest from two vineyards and unacceptable tainting of wine made from grapes of another vineyard.

To date, thousands of acres in Napa, Solano, Sonoma, Mendocino and Fresno counties have been quarantined by the California Department of Food and Agriculture.

Napa County Agriculture Commissioner Dave Whitmer e-mailed his perspective to Wines & Vines: “This pest can be (and probably has been) moved around through traditional industry practices. So, while we are working hard to suppress the populations where found, it will be important for the industry to come together around good quarantine practices that will ensure we are not creating new infestations. The quarantine effort will require some changes to historic practices, but if we all work together, we can prevent the spread of this significant pest to Napa County, California and indeed the nation.”

The Technical Working Group (TWG) also found in retrospect that damage now attributed to EGVM (Lobesia botrana) was observed in those fields as early as 2007, and yields in the most heavily damaged vineyard have been declining steadily since 2005.

Trapping suggested a major center of infestation in the Oakville area, with a second, smaller center in Napa, two to three miles east of the downtown area, plus smaller numbers of moths in several other Napa County and Sonoma County locations.

All members of the group believe that EGVM represents a serious threat to grapegrowing industries in California and beyond. Insecticide use in Napa vineyards is currently light, and most grapes come to maturity with no insecticide applications, but the long-term presence of EGVM would require intensive management including insecticides.

For now, the group agreed that the program should proceed as if eradication is the goal. To do so will leave all options on the table for future consideration.

The group believes that eradication is a realistic goal for the program if (1) the population is not (and does not become) substantially more widespread than it is known to be at present; (2) the grape industry remains behind the effort; and (3) control methods that are available at the present time remain available for use by the program. 

Using insecticides

Those methods include insecticides (insect growth regulators and more conventional products as well as organic alternatives), mating disruption, and the removal of fruit and flowers from grapevines. Initial control efforts consist of ovicides and/or larvicides applied by growers to infested vineyards, followed by mating disruption applications.

At this point, grower participation is voluntary. If this program moves fully towards eradication, a well-coordinated, area-wide effort will be needed to ensure success. Populations could persist and build in vineyards of growers who choose not to participate, jeopardizing the entire project. In addition, treatment areas will have to encompass all habitats that may contain EGVM hosts, including urban and riparian (or other wild) portions of the infested area.

The TWG members agreed that grapes are the major concern, and that EGVM is rarely found on other hosts except Daphne, D. gnidium. Olive trees sometimes act as a host in Europe, and their status as a host in California is unknown but unlikely to support year-around moth reproduction.

Wild grapes, including indigenous and “feral” varieties, are common in the Napa area, including along waterways, and must be considered too, especially if eradication is the goal.

Overall, the risk of EGVM being moved in soil adhering to farm equipment was viewed as very low. Despite this, the TWG recommends that all farm equipment be cleaned before moving among vineyards. EGVM life stages also can potentially be carried on equipment without soil.

The insects will infest second-crop grapes. They should be considered in treatment.

Regulatory recommendations

1. Nursery stock: For grape nursery stock produced within the regulated zone: (1) vines shall be kept free of flowers and berries (this is especially critical if vines are shipped in potting medium rather than bare root); (2) rootstock and scion wood cuttings, as well as dormant rootings and bench-grafted vines, shall be treated with a hot water dip (5 minutes at 127ºF). If nursery stock is to be shipped outside the regulated area, it should also be inspected and found to be free of Lobesia prior to shipment.

2. Grapes for crushing: Moving grapes from even very lightly infested vineyards (with no apparent population) into uninfested areas for crushing can start infestations that then spread into surrounding areas.

If grapes are to be moved out of regulated areas:
• Vineyards in the regulated area must be inspected and found to be free of EGVM prior to harvest.
• Trucks or containers holding grapes must be covered.
• All containers and truck bodies will be thoroughly cleaned at the processing facility.
• Loads from the quarantine area shall be given priority at the processing facility.
• All equipment leaving fields from within the infested area shall be cleaned before, during and after the harvest.
• All winery waste and unfermented pomace must be disposed of in a manner that prevents survival of any life stages of EGVM. Acceptable disposal methods include approved composting on site, chipped, ground or shredded, held in approved containers prior to shipment to an approved facility by an approved hauler or treated in another approved manner such as heat. Material that has been fermented is exempt.

The TWG is optimistic based on experience in Chile that if growers judiciously follow recommendations regarding application of control measures in their vineyards, populations will be reduced to the point where disruption of normal harvesting and grape processing operations will be minimal.

Treatments for commercial areas

Grapegrowers within the infested area have begun spraying insecticides and applying mating disruption, but it may become mandatory. Properly timed applications of insecticides that function as ovicides and/or larvicides should be applied at least to the first two generations. If insecticides are applied to the last generation of the summer, ovicidal properties and proper timing become critical, as larvae feed within large bunches of grapes and thus are difficult to reach with insecticides.

For conventional growers, insect growth regulators such as methoxyfenozide (“Intrepid”) have proven very effective against EGVM in other areas and are less toxic to many non-target organisms than conventional neurotoxins.

For organic growers, TWG members from EGVM-infested countries report that spinosads are the materials of choice, although Btk is an alternative. All vineyards within known infested areas, as well other areas containing potential hosts, should be treated.

The program should also recommend treating areas with grapes and other hosts for a distance of up to 1,000 meters beyond the areas that are known to be infested. The program should consider treating olives during the first generation if olives are found to host EGVM in California, and should pursue registration or exemption to use spinosads or Bt for that purpose.

Mating disruption: Mating disruption treatments should be applied to all vineyards within the known infested area. The TWG recommends against using mating disruption as a “prophylactic” treatment beyond the known infested area, because it will seriously compromise detection capability.

However, riparian and other non-crop areas within the known infested zone should be treated if there is a chance they contain EGVM hosts. In addition, mating disruption functions best when applied across broad areas; small treatment blocks should be expanded to a minimum of 10 acres, and small buffers (25-30 meters) can be applied where practical beyond the edges of treated areas.

In 2010, mating disruption treatments should be in place before emergence of adults of the second generation. This probably means by late May -- right about now -- though monitoring should be used to ensure proper timing.

Host removal (whole plants or susceptible tissues such as grape flowers and berries) in non-commercial areas should be considered as an adjunct to, or, for environmentally or socially sensitive areas, in lieu of insecticide treatment.

Many questions remain, however, and more research is needed, according to the TWG. For the complete report, click here.

The compliance agreements for growers, haulers and wineries are not yet posted to the web. Contact the Napa County Agriculture commissioner’s office to get them.

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