Issue link: https://read.dmtmag.com/i/705606
1 6 V I N E YA R D & W I N E RY M A N A G E M E N T | J u l y - A u g 2 016 w w w. v w m m e d i a . c o m n early April, the Napa Valley Register reported detec- tion of a glassy-winged sharpshooter (Homalodisca vitripennis) egg mass by Napa County Agricultural Com- missioner staff during a routine inspection. The viable egg mass, accompanied by roughly 50 older, non-viable masses, was found on a tree shipped from a Riverside County nursery. This discovery is the second in Napa County this year and indicates transmittance of Homalo- disca vitripennis (Hv) continues to be a very real threat to the region's vineyards. Native to the southeast Atlantic and Gulf states, the glassy-winged sharpshooter first made headlines as a problem species when it was transmitted to South- ern California in the 1990s. It quickly devastated that region's wine grapes as a vector for the Xylella fastidio- sa bacteria, which causes the incurable Pierce's disease (PD) in grapevines. California's screening and control programs contained and now limit Hv from spread- ing further within the state, but, occasionally, it slips through and makes an appearance elsewhere. Quickly forming large populations, flying long distanc- es, being a voracious feeder and serving as a disease vector for numerous crops make Hv a formidable agricul- tural pest both in California and the southeastern states. "[Hv] is an effective vector for Pierce's disease because it's more mobile than other leafhoppers that can trans- mit the bacteria," describes a California Department of Food and Agriculture brochure. Once established in a new area, the spread of Hv may be slowed using biolog- ical or chemical controls, but it's essentially impossible to eradicate. The most common biological control is the release of parasitic Gonatocerus wasps, which prey on Hv egg masses and destroy approximately 90% to 100% of them in its second, late summer or early fall reproduc- tion cycle. Chemical control primarily involves appli- cation of neonicotinoid pesticides to the vineyard. Pesticides generally check population growth and the spread of PD, but impacts to beneficial insects such as parasitic wasps and honeybees are increasingly con- troversial. Currently, PD treatment or prevention methods don't exist. But that could soon change. Texas A&M scien- tists have isolated four bacteriophages that prey on Xylella fastidiosa, created an inoculum comprised of these predator viruses and deployed the inoculum in both Xylella fastidiosa-infected and non-infected grape- vines. The results indicate great success in both situa- tions. "In this study, we demonstrated the therapeutic and prophylactic efficacy for the application of a cocktail composed of four virulent phages," states the Control of Pierce's Disease by Phage report by Mayukh Das et al. "The phage cocktail reduced the pathogen levels in [infected] grapevines and prevented PD symptom development." This research could eventually generate a commer- cially available PD control. Until then, the best method to prevent or control PD is vigilance, starting with Hv. Learn how to spot the insect at all life stages and fre- quently inspect the vineyard and all incoming nursery stock. Their egg masses are laid on the underside of leaves, so look carefully. If evidence of Hv is found at a new site, act quickly and contact the local agricultural commissioner or extension agent immediately. BY JANICE CESSNA Status of Glassy-Winged Sharpshooter and Pierce's Disease Research Now taking entries! Est. 1990 TM Early Bird Deadline: September 15, 2016 Deadline: November 14, 2016 Judging: November 15-16, 2016 Enter: winecompetitions.com The glassy-winged sharpshooter (Homalodisca vitripennis) is the culprit behind the spread of Pierce's disease among grape- vines. The insect infects the plant with the bacterium Xylella fastidiosa when it feeds on the sap from the xylem tissue of a vine. [Photo by Reyes Garcia III, USDA Agricultural Research Service, United States]