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Grapevine Moth Unlikely to Damage Olive Crops

 
By Caroline J. Beck
08/01/2010

The European Grapevine Moth (EGVM) has dominated agricultural news in the wine business since 2009, but it has only recently begun to receive attention among olive growers - and for good reason. The pest can wreak havoc in vineyards, wiping out entire crops in one season, but to the best of our knowledge, they have yet to cause damage in an olive orchard. Understanding the life cycle of the pest helps to explain why the olive industry should be aware of this problem, but has little to fear at this point.

The European Grapevine Moth (EGVM), also known as Lobesia botrana is a serious pest of grapes, causing significant damage to the flowers and berries of vines. Native to Southern Italy, it has been discovered in vineyards all around the world. Most recently, some evidence in the Napa Valley region of California has elevated news of this pest in wine-growing regions of the United States.

The EGVM undergoes 2-4 generations per year depending on temperature. It is the second and third generation larvae, not the adult moths, which can damage and destroy vineyard grapes. News of this pest spread among the olive community when it became known that, in addition to vineyards, olive trees, Olea europaea, are consider to be a primary, though not preferred, host for first generation EVGM to feed on. The most destructive behavior of the EGVM happens in vineyards in the second and third generation cycle, when they invade the fruit, feeding off the grape and leaving behind the potential for a fungal infection that can destroy entire crops.

“The way we see it, it’s called EGVM for a reason. Its preferred host is the grapevine. If you have olives growing in very close proximity and they are ahead of the vineyard in their flowering cycle, you might see it on the olive tree before the vine,” stated Greg Clark, Assistant Agricultural Commissioner for Napa County, California.

First generation larvae typically occur in May and June and feed on developing flower clusters, laying flat eggs .03 inches in diameter in a single line. From research completed in Greece in 1990, there was evidence that larval development is significantly faster on olive trees than grapevines and olive trees that adjoin vineyards are most likely targets.

What is critical to understand, though, is that the olive tree cannot support the second and third generations of the pest, and will leave the olive host to seek out grapevines. The greatest risk to an olive grower is a potential reduction in yield, but at this point, experts agree that it is highly unlikely to become a significant factor.

“The first generation, or first life cycle, is eggs and larvae, when eggs could be laid on olive flowers and then the larvae develop on the flowers and pupate. Moths that emerge from this first generation will seek out grapevines and stay through their second and third, and sometimes, fourth generations. Importantly, olive trees cannot sustain EGVM life in second and third generations. And EGVM are not strong flyers, so they will not return to olive trees to overwinter,” said Monica L. Cooper, an expert on the EGVM and Viticulture Farm Advisor for UC Cooperative Extension.

“The European researchers who have been studying the EGVM for some time have said that, even in the lab, they can’t get the pest to complete its life cycle in olives,” added Cooper.

According to Walt Bentley, University of California IPM Advisor, while it is very unlikely that the EVGM will affect olive yield, attentiveness and proper pest management may become increasingly more important, especially for coastal regions like Napa and Sonoma Counties. For growers who have adjacent olive orchards and vineyards, the problem is one to keep an eye on. On June 22, 2010, a Federal Domestic Quarantine Order was issued that affects certain counties in California and a range of plants, including olive trees. For further details and specific EGVM information, see the USDA site.