Grapevine Moth Continues Retreat

Speakers at Napa Viticultural Fair cite limited damage to 2010 wine crop; vigilance still required

by Paul Franson
Napa, Calif. -- Last week at the Napa Valley Grapegrowers’ Viticultural Fair, the organization’s biennial local trade show, Napa County farm advisor Monica Cooper and Napa County assistant agricultural commissioner Greg Clark reported substantial progress in the fight against the latest invasive vineyard pest, which completely devastated some vineyards’ crops in 2009.

VIDEO: Monica Cooper discusses moth suppression

No one thinks the war is completely won, but it appears that in only one year, Napa Valley grapegrowers, county officials and University of California farm advisors have turned the European grapevine moth (EGVM) from a huge threat into simply another pest to be monitored.

This insect is especially troublesome because it destroys grapes; Most other pests damage vines but don’t affect current crops.

Grape bunch sensors and weed flamers

VIDEO: Stuart Weiss on monitoring microclimates
Beyond grapevine moths, other seminars at the well-attended Napa Valley Viticultural Fair covered weed management and cover crops, strategies for in-vineyard insectaries, and in Spanish, what vineyard workers need to know about grapevine diseases and vineyard practices for winter.

Six supplier companies and the Bay Area Air Quality Management District each presented outdoor demonstrations about their techniques, products and in the one case their regulations.

Stuart Weiss and Carrie-Anne Kunkel of Vineyard technology company Viticision, Menlo Park, Calif., demonstrated its equipment and techniques for measuring and modeling micro-climates with sensors placed in grape bunches, precision photography and software.

VIDEO: Mark Twitchell demonstrates weed flaming
Mark Twitchell of Allied Propane Service, Napa, Calif., showed how to use its vineyard flaming equipment for weed and insect control.

Other presenters included Pacific BioControl, Suterra, Sebastopol Tractor Co., and Rainbow Agricultural Services. The fair also included many booths showing local, regional and national products designed for use in vineyards.

The session attended by a capacity crowd of growers and vineyard workers included a scary video showing the moth swarming over vines last year like a scene from a low-budget horror movie. The crop from that vineyard in Coombsville was completely destroyed; this year, no EGVM were found in the vineyard.

Detection monitoring, followed by use of mating disruption pheromones and application of either organic or conventional insecticides were the growers’ primary weapons. A quarantine during harvest may have helped, too.

Clark noted that when EVGM appeared last year, the county placed 5,100 traps around the county. These proved to be very selective and isolated the primary pockets of infestation from Yountville to St. Helena and Third Avenue (Coombsville) as well as north of Calistoga, Napa and north of Napa and Carneros. Some moths were discovered in every town in the county.

In 2009, the traps yielded more than 100,000 EGVM. The bugs also were found in nine other counties, but in very small quantities so far -- only 200 spread over many counties. Based on Napa’s experience, those counties will likely undertake campaigns to fight them next year.

Inspection is more difficult because three generations of the moth are produced in a year. However, prompt action resulted in a dramatic reduction in populations, from 100,000 for the first generation in 2010 to 1,300 in the second and only 273 in the third.

This year, UC Cooperative Extension deployed 38 monitoring traps in the key areas, Oakville, Rutherford and Napa city's Third Avenue area, in vineyards with known populations. They were checked three times weekly. Other delimitation traps designed to locate the moths were reduced to seven per square mile, and checked every 14 days.

Insecticides and mating disruption

European Grape Vine Moth
European Grape Vine Moth traps like this one from 2010 are deployed in key areas. Photo by Jack K. Clark

The county initially discouraged grower trapping until the extent of infestation was determined, then allowed it after the limits were determined. Once the infested areas were isolated, a combination of insecticide treatments and mating disruption controlled the EGVM.

Best results were achieved when growers treated all three generations and used mating disruption, especially for organic vineyards since organic insecticides are less potent against this pest. Proper timing was critical; again, especially for organic materials that don’t last as long. Growers were warned that it is also important to treat before damage or EGVM were seen.

About half of the vineyard acreage in Napa County (21,327 acres) was treated at least once. Total treated acreage (vineyards plus other areas) was approximately 96,000 acres. About 6,000 acres were treated with Isomate: EGVM mating disruption lures. The treatment regimen resulted in excellent control in most cases.

A new element of the control plan was a quarantine to ensure that moths weren’t transported across the county (which probably affected other areas in California). The ag commissioner’s office issued more than 900 compliance agreements, and performed more than 130 inspections of growers, haulers and wineries and another 150 inspections/certifications for other regulated entities.

In addition, the ag commissioner’s office inspected and certified 24 shipments -- 266.5 tons of winegrapes -- using USDA Fresh Fruit protocols; 103 tons were fumigated.

Clark reported that overall, there were very few problems with people not doing what they were supposed to do.

One continuing concern is grapes in urban areas. The ag commissioner’s office conducted intensive outreach to the community and industry, and used Dipel or removed flowers and fruit of grapevines within 200 meters of all EGVM finds, as well as deploying mating disruption. Office personnel even collected grapes from the abandoned vines at Copia, the closed museum in downtown Napa, as reported in the local Napa Valley Register as a reminder to others outside the winegrowing industry.

Local research details treatment
Monica Cooper, the entomologist and vineyard advisor from UC Cooperative Extension, reported interesting findings beyond the suppression of the moths. Ironically, these interfered with her attempts to better understand the pest.

This research determined that grapevines are the main hosts; another host Daphne gnidium, doesn’t appear to be present here. Researchers found no eggs, larvae or pupae on any blackberries, elderberries or rose hips. Native grapes don’t seem to be factors.

Two insecticides were applied in one trial on the second generation of moths at egg hatch (June 8). When the larvae emerged (June 25), both Intrepid (12 ounces per acre) and Altacor (3.25 ounces) were effective at the middle of the recommended usage dose to kill eggs as well as larvae. No live larvae were found.

Conventional Altacor and Intrepid were more effective than organic Dipel (Bt) and Entrust, and the latter required more frequent applications. Timing is critical: Larvae appear about three weeks after the eggs are laid. The pesticides worked if sprayed only on the larvae, however. Cooper said, “They’re very effective insecticides.” She added that they don’t seem to disrupt natural predators of the moths.

She suggested spraying one application of conventional insecticides, or two or three of organic, for the first generation of moths to catch egg hatching, followed by one conventional treatment (or two organic) of ovicicdes three to five days after the first month is caught, and larvicides at egg hatch 14 days after the first month is caught. Then use ovicides during the peak flight period, the time of peak egg laying, which is 10 to 14 days after the first month in a generation is caught. Couple this treatment with mating disruption.

Mating disruption worked best when the density was 200 lures per acre. They worked best when populations were low, and the vineyard not too steep. They’re best used for a large area, not small vineyards. All three (Alpha Scents, Suterra and Trece) worked well, but some lasted longer than others.

Cooper also noted. “We’ve done the easy part. We’ve caught the easy ones. We’ll have to make more efforts next year and for a few years to come.” She suggested trying larvicides rather than focusing on ovicides next year, however. For more details, visit the Napa County Cooperative Extension.

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