Agriculture officials in Tuolumne and Calaveras counties are closely watching the spread of the European grapevine moth, a plant pest that poses a particular threat to the state’s estimated $61.5 billion wine and table grape crop.
The moths and their larvae were first detected in an Oakville area vineyard in Napa county in 2009. Since then, they have turned up in six counties.
Most recently, two moths were found in a vineyard east of Lodi. This find is particularly concerning for Calaveras County ag officials and vintners, since several wineries import grapes from Lodi. Tuolumne County wineries do not accept grapes from other counties.
If the moths get established in Calaveras County, they would devastate the county’s $3.36 million grape crop, and could affect other plants like peaches, olives and pomegranates.
In Tuolumne County, about $200,000 worth of grapes annually are at stake.
The moths threaten plants in two ways. First, they destroy fruit by damaging grapes’ skins. That damage also leaves the fruit open to secondary fungal and bacterial infections that can spread to and wipe out an entire crop, said Kevin Wright, Calaveras County’s deputy agriculture commissioner.
Efforts at controlling the moth in Calaveras and Tuolumne counties have thus far focused on monitoring. Calaveras has taken the additional step of having grape growers and processors sign compliance agreements.
The costs of monitoring for European grapevine moths is being paid for entirely by the state and only involves one trapper per county.
Since April, 14 vineyards in Tuolumne County and 56 vineyards in Calaveras have been equipped with phermone traps — small tent-like contraptions which would attract and trap the moths should they arrive at a vineyard. The traps are spaced every 40 acres and checked every two weeks.
If two of the grapevine moths are found within three miles of each other, all the vineyards within a five mile radius of the find will be quarantined.
To further ensure the quality and safety of grapes in the state, farmers, transporters and wine producers are working together to make sure they are all in compliance with a moth treatment-compliance agreement.
“Certain procedures must be followed,” Wright said. “But if everyone does what they are suppose to do there should be no movement of EGVMs into the county.”