What is in this article?:
- Lucia Varela, UC North Coast IPM advisor in Santa Rosa, Calif., told the 39th annual CAPCA conference that she is “cautiously optimistic” that a major EGVM infestation in the Napa Valley has been turned back.
- EGVM was first identified in Napa in late 2009 where it destroyed the wine grape crop in at least one vineyard.
- Possibility: EGVM found its way into the North Coast on plant material or machinery imported from Chile.
Key to knockout
One of the keys for the quick, apparent knockout bunch in California was treatment of the first generation of moths. That first generation, Varela said, does not do much damage to the grape flowers, and vines often compensate if the worms cause damage.
However, that first generation, left uncontrolled, can explode into berry-damaging second- and third-generation larvae.
Europeans do not control that first generation, she said, because it does not cause damage. That could be the primary reason EGVM widely infests so many areas across the Atlantic.
Another key factor playing into California getting a quick handle on this pest is that it only feeds on grapes. It can be found in other crops, however, but does not thrive on anything but grapes.
Spurge laurel is a preferred EGVM host in Europe, but that plant is not found in the U.S. except in Washington state forests. Varela said it is imperative to keep that plant out of California.
Varela said the pest is relatively easy to control, since it does not travel far. It is not a strong flier.
Unlike its cousins in the tortrix family, EGVM moths lay only one egg. However, a single female can lay more than one egg in her life cycle. This single egg lay often localizes damage in a grape bunch to three or four berries.
Although the first generation does not damage flowers, it can build webbing. It is the second and third generations that feed on berries, penetrating the skin and causing bunch rot.
UC entomologists recommended a very aggressive control program where first-generation moths were trapped. Altacor and Intrepid were the preferred pesticides, although Avaunt, Success and Delegate also offered control.
UC worked off a European-degree model to time peak EGVM emergence, but the model was found to be off a bit in the start and end of generations. Varela said this model is being revised for next season and will be available on the UC IPM website.
Regardless, emergence of the first generation of worms can be very drawn out. Last season growers often times treated twice to catch as much of that first generation as possible. With a new degree day model, Varela said growers can better time that first spray to catch peak larvae emergence and may forego a second spray.