For the third time in a month, Napa County agricultural inspectors have found glassy-winged sharpshooter egg masses on ornamental plants recently brought into the county.
The first two discoveries--on Feb. 9 and Feb. 14--occurred on ornamental plants offered for sale at local retail plant vendors. In both cases the plants had originated in Ventura County, an area known to have been infested with the glassy-winged sharpshooter for several years. But the latest sighting was made March 10 at a landscape job location in the community of Angwin, located in the hills on the eastern side of Napa Valley.
The leaf-hopping insect, which transmits the vine-ravaging Pierce's disease, is believed to have entered California in the early 1990s, most likely on nursery stock imported from Florida. In 1998, the pest infested and devastated the Temecula Valley grapegrowing region in Riverside County.
To date, county and state agriculture officials have managed to slow the insect's spread northward by implementing a series of protocols that include regular nursery inspections both at point of origin and point of sale or use. Napa County has reported no more than three egg clusters in any one year, so the appearance of three clusters in less than a month is some cause for alarm.
The latest cluster was found on one of 250 1-gallon periwinkle vines that had come from a nursery in Lodi, thought to be an uninfested area. But the vines had originated at nurseries somewhere in Southern California, most likely in either Ventura or Los Angeles counties. The Lodi nursery picked up the entire shipment of vines the next day and returned them to Lodi.
"We are very concerned that plant material continues to come into Napa County with glassy-winged sharpshooter life stages on it," said Greg Clark, assistant Napa County agricultural commissioner. "We can quote statistics and say that the overwhelming majority of plants shipped out of infested areas are clean, but any egg masses in Napa is unacceptable."
Clark went on to say that Napa is the only county in the state that inspects shipments coming from uninfested areas, such as Lodi. "People always want to know why [we inspect all shipments]," he said. "Well, this is why. It's the first time we've found eggs on plants from an uninfested area. This is still as much an issue today as it was five years ago, and people need to understand that."
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