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Grapevine Pests Discovered in Nursery Shipments

July 2014
by Paul Franson
Glassy-winged sharpshooter
Glassy-winged sharpshooter spreads Xylella fastidiosa, the causal agent of Pierce's disease. Photo: Jack Kelly Clark/University of California

Napa, Calif.— On the morning of May 22, inspectors from the Napa County Agricultural Commissioner’s office discovered two viable glassy-winged sharpshooter egg masses during a shipment inspection at a local plant retailer. In addition to contacting the California Department of Food and Agriculture (CDFA), Napa officials notified authorities in other counties, and throughout the day at least five California counties identified glassy-winged sharpshooter (GWSS) eggs in shipments originating from the same plant broker in San Diego County, Calif.

The sharpshooter insect is a notorious vector for spreading Pierce’s disease to plants in cluding grapevines. Eggs were discovered in crape myrtle trees that were part of shipments to Sutter, San Mateo, Napa, Sonoma and Sacramento counties, according to Humberto Izquierdo, the assistant agricultural commissioner in Napa County. Three infested shipments were identified in Sacramento County, and all of the counties where GWSS eggs were discovered grow grapevines commercially.

Napa County inspectors found egg masses on two different crepe myrtle trees. The samples were driven to the CDFA lab in Sacramento, Calif., for identification and to determine viability. A CDFA entomologist determined both egg masses to be viable sharpshooters. Eggs discovered in Sacramento County also were determined to be viable, while those found in Sonoma County were not. Lab results from the other counties were pending.

Staff from CDFA’s Pierce’s Disease Control Program began an investigation May 30.

“This recent discovery of viable GWSS egg masses points to the continued importance of our GWSS exclusion and detection programs,” said Napa County Agricultural Commissioner Greg Clark. “We will work with CDFA and counties throughout the state to ensure the effectiveness of the GWSS program and have Napa County inspectors remain vigilant inspecting plant shipments.”

The contaminated shipment originated from a north San Diego County broker-nursery that is not located in a GWSS-infested area but may have included plants from other Southern California counties. The nursery shipped plants to 30 different retailers in 13 counties—most of them in Northern California and a few in California’s San Joaquin Valley. The compliance agreement issued to the particular nursery did not require the plants to be treated with an insecticide.

Napa County wrote a notice of rejection for all of the plants delivered. The crape myrtles were picked up around 1:30 p.m. on May 22, and the rest of the plants were picked up for return to the shipping nursery May 23.

The investigation by CDFA and the San Diego County Agricultural Commissioner’s Office is ongoing and will determine the breakdown in protocols that led to the trees being sent to Northern California with viable GWSS egg masses.

The San Diego County nursery has been fined for violations in the past, but the San Diego Agricultural Commissioner’s office did not identify it due to the ongoing investigation. The nursery may have its shipping privileges suspended and may face administrative civil penalties including fines and suspension. Jim Wynn of the San Diego Agricultural Commissioner’s Office said his department hoped to complete the investigation in a few weeks.

Other counties may also seek action against the nursery. “We want aggressive action to send a message that this behavior is unacceptable,” Clark said. “It’s a huge threat to an important industry.”

Though the insect is common in Southern California and in pockets elsewhere, Napa County has excluded it for almost 15 years by mandating rigorous inspections and quarantine while fostering cooperation between the Ag Commissioner’s Office, UC Extension specialists and local growers. Only egg masses have been found, and those were excluded except for one adult female in an incoming shipment in 2007.

Unlike some counties that inspect only shipments they are notified of, Napa inspects all plants—even those from areas free of pests.

The county is continuing an aggressive educational campaign against the sharpshooters, and its Board of Supervisors recently designated May as glassy-winged sharpshooter awareness month. Homeowners are asked to buy their plants only from certified Napa County plant retailers where plants are thoroughly inspected for any signs of GWSS or other serious pests.

Clark also stressed that the Pierce’s Disease/GWSS Program is up for renewal. The California Assembly passed AB 1642 on May 27 without a single “no” vote. AB 1642 would extend the Pierce’s Disease/Glassy-winged Sharpshooter Program for another five years, subject to a favorable industry referendum in spring 2015. Action in the state Senate is pending.

The glassy-winged sharpshooter is an invasive pest from the southeast that was inadvertently introduced into southern California in the early 1990s, most likely as egg masses on ornamental or agricultural plants.

It is a large leafhopper that obtains its nutrients by feeding on plant fluids in the water-conducting tissues of a plant (the xylem). The real problem associated with the glassy-winged sharpshooter is that it can spread the disease-causing bacterium Xylella fastidiosa from one plant to another. This bacterium is the causal agent of Pierce’s disease, a devastating ailment for grapevines.

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