New grape pest threatens North Coast

Since the discovery of the European grapevine moth, Lobesia botrana, last month in Napa County, local agricultural officials have been working with the USDA, the California Department of Food and Agriculture and industry groups to better understand this invasive pest and how best to respond to this latest threat to the state’s grape industry and other fruit producers.

“Our biggest challenge is developing and implementing pest management strategies that will lead to its eradication,” says Greg Clark, Napa County’s Assistant Agricultural Commissioner.

These efforts include the help of the Napa Valley Grape Growers Association, Napa Valley Vintners, Napa Sustainable Wine Growing Group, Napa Valley Vineyard Technical Group and Napa County Farm Bureau.

Pupae of the small multi-colored moth, no more than about 3/10 of inch long with a wingspan of half-an-inch or less, were originally found in last October, by a grower in a vineyard near Oakville-- the first known time that the moth has been found in the United States. Efforts to positively identify the pest were hindered when the pupae failed to emerge. However, researchers were able to rear larvae collected from the grapes in the same area this fall and use DNA technology, which had previously been unavailable, to confirm the pest’s identity.

A native of southern Italy, the moth is now found throughout Europe, North and West Africa, the Middle East, and eastern Russia. More recently, it was introduced into Japan, and last year, for the first time, it was reported in Chile.

Larvae of the European grapevine moth feed primarily on the flowers and fruit of vines. However, they also feed on other hosts, including blackberries, cherries, nectarines and olives.

In May and early June, first-generation larvae web and feed on the flower clusters, while second-generation larvae feed on green berries in July and August. Young larvae penetrate the berry and hollow them out, leaving the skin and seeds. The worst damage is caused in August and September when third-generation larvae create webs and feed inside berries and within bunches, which become contaminated with frass. Feeding damage to berries after veraison also exposes them to infection by Botrytis and other secondary fungi. What’s more, the damaged berries can attract other pests, such as fruit flies and ants.

So far, the European grapevine moth has been found at 27 locations in Napa County – 21 in the Oakville-Rutherford area, three east of Napa and two south of St. Helena. “We’ll have a much better idea of how widespread the moth is next spring when we set out traps to catch the first flight of moths after they emerge as adults in April or early May,” Clark says.

A statewide survey to detect any moths is being planned, he notes.

In the meantime, Clark advises growers to remove any grapes left on or under vines, and disk them in to reduce populations of any overwintering larvae. Currently, no regulatory quarantine programs are in place. However, he notes, they are likely given the seriousness of this invasive pest introduction into North America.

The moth population spends the winter in the pupal stage. You can check your vineyard for the presence of pupa by removing bark from vines, suggests Lucia Varela, North Coast IPM Advisor with the University of California Cooperative Extension. “Usually, the pupa is inside a white cocoon which is stuck to the wood underneath the bark,” she says. “If you find a pupa, take it to your county agricultural commissioner’s office for identification.

“Typically, when a pest like the European grapevine moth, is detected for the first time in the United States, it has come in on something like equipment or infected nursery stock,” Clark adds. “We’re concerned that it might have been brought in illegally on plant material prohibited from entering the country. That works against the interest of other growers, the industry and the community.”

TAGS: Grapes
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