With the threat of a more widespread Pierce’s disease epidemic looming, UC scientists are working on a variety of fronts to prevent and cure this fatal bacterial plant disease, the July-August issue of California Agriculture reports. The current issue of California Agriculture can be viewed on-line at: http://danr.ucop.edu/calag/

Pierce’s disease has been present in California since the 1880s, but introduction of the nonnative glassy-winged sharpshooter in the 1990s hastened the spread of the bacterium Xylella fastidiosa that spreads the disease. Pierce’s disease destroyed as much as 800 acres of wine grapevines in the Temecula region (Riverside County), but also poses a threat to raisins, table grapes, almonds, alfalfa and other crops, as well as oleander and other ornamentals. Populations of glassy-winged sharpshooter have been discovered in at least 13 counties.

A $10 million, multidisciplinary research effort is under way to develop solutions to this challenging problem, with dozens of UC scientists collaborating on agrochemical and micronutrient treatments, biological control, genetic engineering and other approaches.

Peer-reviewed findings reported in the July-August issue of California Agriculture include:

* Proximity to citrus: In Temecula Valley, scientists believe that the spread of Pierce’s disease in grapevines may be related to their proximity to citrus groves. Because glassy-winged sharpshooters inhabit citrus groves in large numbers, growers should take additional care with vineyards located nearby. Contact: Thomas M. Perring, UC Riverside, (909) 787-4562 or thomas.perring@ucr.edu.

* Egg-laying behavior: While depositing eggs, the female glassy-winged sharpshooter forms white spots on its forewings from secretions known as brochosomes. Understanding behaviors associated with brochosomes could provide important new directions for controlling the insect’s spread. Contact: Raymond Hix, UC Riverside, (909) 787-2064 or rhix@citrus.ucr.edu.

* Insecticide trials: A field comparison of various insecticides found that the pyrethroid and neonicotinoid classes are most promising for control of glassy-winged sharpshooter. Chemical controls can provide a stopgap measure for limiting its spread while new integrated pest management programs are developed. Contact: David Akey, USDA, (602) 437-0121 x245 or dakey@wcrl.ars.usda.gov.

Also in the May-June issue of California Agriculture:

Roads a major sediment source in North Coast rangeland: To protect water quality, federal regulations require Northern California ranchers to evaluate and mitigate the potential for sediment to be deposited into streams. A comprehensive survey of 117 North Coast sites on 10 ranches found that land managers can achieve the greatest reductions in sediment generation by focusing on erosion from roads. The authors also noted, "The established [federal] criterion of 10 cubic yards resulted in the inventory of 35 sites that represented less than 1% of the total deliverable sediment in this survey. Raising the threshold to 100 cubic yards would identify over 99% of the deliverable sediment from the surveyed sites, reduce the number of sites requiring inventory and allow reallocation of time and funds for soil conservation and sediment delivery prevention." Contact: David J. Lewis, UC Davis, (707) 565-2621 or djllewis@ucdavis.edu.

New closterovirus identified in grapevines: In recent years, grape growers have used grafted plants to overcome site-related problems. However, scientists discovered that popular ‘Redglobe’ table grapes planted on rootstock were declining and dying. Using greenhouse and field experiments, as well as RT-PCR assays, UC scientists identified a new graft-transmissible closterovirus called Grapevine rootstock stem lesion associated virus (GRSLaV). Contact: Jerry Uyemoto, USDA/UC Davis, (530) 752-0309 or jkuyemoto@ucdavis.edu.