Across the United States from California to Florida and as far north as Virginia, grapevines

Across the United States from California to Florida and as far north as Virginia, grapevines are succumbing to Pierce’s Disease (PD) which currently infects more than 30% of grapevines and is a threat to the $30 billion wine industry. PD is caused by the bacterial pathogen, Xylella fastidiosa, which blocks water from flowing through the xylem of plants. Affected grapevines develop leaves that are discolored and dried out, and usually die within 2-5 years. X. fastidiosa is transmitted by xylem feeding insects. The most effective insect vector is a leafhopper, Glassy-Winged Sharpshooter (GWSS, Homalodisca vitripennis). GWSSs are able to survive in mild to scorching temperatures and can feed on the woody stems of plants, making them an optimal vector of the pathogen. In the summer, GWSS populations explode, creating the greatest period of X. fastidiosa infection of grapevines. During summer, 2010, we performed a survey on unsprayed grapevines on the UCR campus to determine patterns of GWSSs visiting the plants and their infection status. Insects were collected on yellow sticky traps from late June to late October. All insects were surface sterilized, the DNA was extracted, and real-time PCR was used to test for presence of X. fastidiosa. GWSS visitation to the plants was highest in midsummer. From 112 insects collected, 83 were tested for X. fastidiosa and approximately 76% were found to be positive. These results indicate that many of the GWSSs feeding on the unsprayed grapevines are infected with X. fastidiosa, placing the plants at high risk of infection.