More than 200 square miles of North Coast vineyards are under quarantine from an infestation of the European grapevine moth (EGVM).
That could grow to cover 9,000 more acres of vineyards in the Kenwood areas of Sonoma County if additional EGVM moths are trapped in Sonoma County where four have already been found.
The California Department of Food and Agriculture (CDFA) initially established a 162-square-mile quarantine including portions of Napa, Sonoma, and Solano counties due to the EGVM infestation. It now totals 219 square miles.
The quarantine specifics are being hammered out by the CDFA. Equipment should be washed and sanitized before moving it to other areas.
The EGVM was first detected last September in Napa County. EGVM, Lobesia botrana, feeds primarily on grapes, but also on other crops and plants. The Napa find was the first in the U.S.
Grapes are the No. 1 California-grown agricultural crop with an annual gross production value of about $3.9 billion.
The first EGVM detection in Napa County was in a trap in the Oakville area. Increased trapping and surveys found additional insects on the eastern side of the city of Napa plus the Oakville, Rutherford, and St. Helena area.
One Oakville-area grower lost his entire 2009 grape crop to the insect.
“This is an invasive moth, something that doesn’t belong in Napa County or anywhere in this country,” said Dave Whitmer, Napa County agricultural commissioner. “We’re doing all we can, working with our state and federal partners, to track this pest and determine our response as quickly as possible.”
Monica Cooper, viticulture farm advisor and county director, University of California Cooperative Extension Service, Napa County, is researching the pest to determine how to control it.
“Some of the eggs laid on the early grape varieties are getting close to hatch (late April) so we’ll have some first-generation larvae,” Cooper said. “The moths are at peak flight right now.”
Cooper is conducting trials to study moth phenology.
“We need to understand the moth for research purposes and to help growers understand when insecticide sprays should be applied,” she said. “I am also conducting a trial on the effectiveness of commercially-available lures for traps.”
The EGVM was found in neighboring Sonoma County on March 29 in the Kenwood area. The Sonoma County agricultural commissioner ordered the placement of 4,000 traps in commercial vineyards.
Three more moths were found in late April near Kenwood and the city of Sonoma. Two moths found within three miles of each other within one lifecycle triggers a CDFA-USDA quarantine, the ag commissioner’s Web site says.
Insecticide products for EGVM control should target the first- and second-generation moths.
Cooper says available larvicidal and ovicidal products offer good activity with a low impact on the natural enemies. Second, if mating disruption is approved, use it for the second flight. Third, train employees on the moth and take samples after spraying.
According to the University of California Statewide Integrated Pest Management (UC IPM) Program, first-generation larvae web and feed on flower clusters in May and June.
Second-generation larvae (July-August) feed on green berries. Young larvae penetrate the berry and hollow it out leaving only the skin and seeds.
Third-generation larvae (August-September) cause the most damage. Webbing and feeding inside the berries and bunches contaminate the berry with frass (excrement). Feeding damage after veraison exposes the berries to Botrytis (fungal rot) infection and secondary fungi.
According to UC IPM, the adult moth is about a quarter inch long (6-8 millimeters). The wingspan is about half an inch (11-13 mm). The female moth is slightly larger than the male.
Male and female moths have mosaic-patterned wings. The forewings are a tan-cream color mottled in gray-blue, brown, and black blotches. The second set of wings is gray with a fringed border. The wings are in a bell shape over the abdomen when the moth is at rest.
Eggs are elliptical, flat, visible to the naked eye, and laid on the fruit. Eggs are initially a creamy white color and turn yellow during embryo development. The eggs turn black when the larva head is formed.
EGVM belongs to the Tortricidae pest family and the sub-family Olethreutinae. Different types of Tortricids can be confused with EGVM moths. Adult moths can be identified by a qualified entomologist.
Cooper says EGVM eggs are laid singly, not in masses. About 35 eggs are laid daily for six to seven days. From 80 to 160 eggs can be laid in the moth’s lifetime. EGVM overwinters as pupae under the bark, not as larvae mummies inside berries or on spurs.
Adult moths fly at dusk when temperatures are below 54 F. The optimum development threshold is 70 F to 84 F. Mating occurs in flight. Most females mate once per lifetime.
• Origin and potential range
No one is sure how the pest arrived in Napa County or its country of origin. Genetic studies could provide answers.
“The EGVM population in Napa County is very similar to the moth population in Chile,” Cooper said. “The genetics on our moth and the Chilean EGVM moth are nearly identical from what we’ve seen so far. We have not yet received any moth samples from Europe for comparison.”
A major question of concern across California’s grape industry: Could EGVM spread to other grape-growing areas?
“Yes it could spread,” Cooper said. “That’s why we are doing the best we can to knock down the populations so it doesn’t spread around the state.”
Elizabeth Emmett, spokesperson for the city of Napa, calls the moth a poor flier.
“The European grapevine moth can only fly about 100 yards on its own,” Emmett said. “The movement of the pest into other areas would require artificial transport.”
A 2003 mini-risk assessment conducted by the University of Minnesota suggests the insect could potentially move to other California grape-growing regions including other coastal areas and the San Joaquin Valley.
The same study suggests the insect could potentially cover the eastern half of the United States.
• Other criteria
EGVM is native to southern Italy. It is a significant grape pest in Europe, Chile, the Mediterranean, Japan, the Middle East, Russia, and northern and western Africa.
Based on findings in other countries, the EGVM host range can include blackberry, olive, cherry, peach, kiwi, pomegranate, cucumber, plum, currant, carnation, persimmon, and grape.
Olive flowers host first-generation moths in Italy and Greece.
According to the UC IPM Web site, EGVM control efforts in other countries tend to target the second generation. Treatments of the first and second generations there are recommended if populations are high or treatments are conducted on an area-wide basis.
For California, UC IPM says first- and second-generation treatments are warranted since the EGVM is a new pest. Insecticides are less effective after bunch closure.
Reduced-risk products registered for grapes in California for Tortricid larvae include spinosyns, insect growth regulators, and Bacillus thuringiensis. Cooper has a complete list available online at http://cenapa.ucdavis.edu/files/77066.pdf.
While pheromone mating disruption products have been effective in small grapevine moth populations in Europe, no mating products are currently registered in the U.S.
Olive plantings around vineyards are a host concern for grape growers. First-generation moths move into olive blooms, but do not attack the fruit.
Valent is requesting a 24 (c) special local need registration from the California Department of Pesticide Regulation to allow the use of the insecticide DiPel DF on olives to reduce EGVM hosting, says Tino Lopez, Valent commercial development representative, Clovis, Calif.