Trouble in Napaland: European Grapevine Moth

The discovery of the European grapevine moth -- scientific name Lobesia botrana -- in parts of Napa County has forced Federal officials to impose a quarantine on areas in northern and southern Napa County as well as parts of Sonoma and Solano counties. The quarantine, announced on March 9th, and covering an area of 162 miles, places the regulation of harvesting, shipping, and handling of certain fruits and plants, inclusive of grapes, into the hands of government commissioners.

Source: SFGate.com

The European grapevine moth, native to southern Italy, has long been a major problem for European grape growers and has extended its reach into North and West Africa, the Middle East, and, recently, Chile and Japan.  It was noticed in the U.S. for the first time when it was detected in a vineyard in the middle of Napa last September.  The entire crop of the vineyard was destroyed before the moth was detected.

The moth is feared because it is a berry pest. The larvae burrows into the fruit and pupates and, in so doing, introduces fungus and rot which destroy the berry.

There is some confusion in the industry as to exactly how this pest will be battled.  According to a report on CNBC.com, "Premium grape growers face the prospect of spraying at least three times in the months ahead to deal with three generations of grape-eating larvae that are produced each season." There would be direct financial impact to the grower if such an approach were pursued as spraying costs run in excess of $200 per acre.  Further, premium grape growers feel strongly that their low-impact farming techniques have contributed significantly to the quality of today's wine and that reverting to high-impact methods could have deleterious effects.

Jenifer Putnam, executive director of the Napa Valley Grape Growers Association indicated (SFGate.com)that there would never be any spraying for this pest. According to Ms. Putnam, "... you have to be more surguical and get right in there with the worm."

A number of steps are being taken to combat the pest.  First, over 750 traps have been placed in the quarantined area and plans are afoot to lay more throughout the growing regions. The traps draw the insects onto sticky strips.  The second ongoing active process is the deployment of mating disruption dispensers.  These dispensers emit a female pheromone which attracts male moths who die after flying around for a while in an agitated state futilely searching for a female moth.  The focused application of pesticides and the introduction of predatory wasps are being considered as future "kill-the-moth" tactics.

With the market issues they confront today, the last thing that Napa grape growers need is the European grape moth.  The average ton of premium grapes cost approximately $3400 and three to four tons of quality grapes are produced per acre.  If uncontained, the European grape moth could have a severely negative impact on Napa's $400 million annual premium grape crop and could force growers to attempt to raise prices in the face of reduced demand for premium wines.