Vineyard Traps Set for Devastating Moth

Alameda County agricultural authorities in the Tri-Valley have begun setting traps to detect a devastating pest that can destroy entire vineyards if left to spread uncontrolled.

The pest is the European grapevine moth, which is responsible for the quarantine of a 162-square mile area in Napa, Sonoma and Solano Counties .  Quarantined areas now include St. Helena and Yountville.

Last fall, an infestation by the moth wiped out the entire nine-acre crop of a grower near Oakville.      

The moth is formally called Lobesia botrana.  It originated in southern Italy and found its way to other parts of Europe, Russia and the Middle East.  It is now found as far away as Chile and Japan.  Its first known appearance in North America was the Napa infestation, discovered in September.

No European grapevine moths have been detected in the Tri-Valley, but the threat is real and being taken seriously, according to Chris Chandler, executive director of the Livermore Valley Winegrowers Association.

Local vintners are well aware of the moth.  The detection effort and the potential damage were discussed in a recent LVWA newsletter and in a grower’s meeting earlier this month, Chandler said.

The Alameda County Department of Agriculture is placing the sticky, triangular traps this week and next, planning to set at least one per vineyard, according to Bob Blumenthal, deputy commissioner in the Alameda County agriculture department.

In larger vineyards, the traps will be set at a rate of about one per 40 acres.  Like similar traps for other insects, they will contain a pheromone, a chemical designed to attract the target pest to flypaper-like sticky surfaces that can hold them fast.

Similar trapping efforts are underway in other counties, especially where grapes are economically important.  “This is a serious threat, not just in Napa County but throughout California,” said Greg Clark, the assistant agricultural commissioner for Napa County. 

The University of California ’s Integrated Pest Management program reports that, beyond grapes, the moth has been found on other crops important to the California economy such as olive, cherry, kiwi and pomegranate.

The European grapevine moth is the second destructive moth to be found in California vineyards in recent years.  The light brown apple moth, native to Australia and found widely in New Zealand as well, was discovered in Berkeley in 2007.  It has since spread throughout the state, prompting quarantines, spraying and public controversy over the merits of various control techniques.

Deputy agricultural commissioner Blumenthal considers the European grapevine moth to be a more serious threat than the light brown apple moth because of its track record, particularly the destruction of an entire vineyard crop in Napa last fall.  The apple moth feeds on foliage, while the European grapevine moth goes for the fruit of the grape as well as other parts of the plant.

Fighting pests is hardly a new task for grape growers, who have to deal every year with a wide and changing range of fungi and insects.  (See related story, Grape Growers to Vote on Vineyard Protection.)  But control of the European grapevine moth is likely to be difficult and expensive because the moth goes through three generations in a growing season, likely requiring three separate treatments for control of serious infestations.

Each generation attacks a different part of the plant.  In May and June, first generation larvae feed on flower clusters.  In July and August, second generation larvae feed on green berries.

Third generation larvae are the most damaging.  They burrow into grapes and clusters in August and September.  In so doing they destroy fruit, but they also create wounds that expose the plant to infection by fungi like the highly destructive botrytis.  They can also attract secondary pests, like raisin moths, fruit flies and ants.

The cost of multiple sprayings may be a serious financial burden for those vintners who are already struggling with reduced revenue caused by depressed wine prices.  Equally important, wine makers whose reputations depend on marketing an organic product, or wines with only the complex of flavors and aromas derived from the natural soil, may be restricted in the treatments available to them.

There are ways to combat the European grapevine moth other than powerful chemicals and insecticides.  Two bacterial formulations that are marketed as natural products to kill larvae are Bacillus thuringiensis and spinosad.  European vintners have reported other approaches as well, such as introducing parasitic flies and wasps that attack the moth pupa during the winter and using pheromones to disrupt mating.