Citrus not harmed by glassy-winged sharpshooter, but could face tremendous IPM losses

The glassy-winged sharpshooter could send 20 years of hard-won integrated pest management progress in citrus down the drain.  That's a concern of Beth Grafton-Cardwell, the UC Riverside citrus entomologist based at the Kearney Agricultural Center near Parlier.  Although glassy-winged sharpshooter does not harm citrus, growers may control the pest to slow its movement into nearby vineyards.  "We need to know whether any of the materials we use on citrus kill glassy-winged sharpshooter and, if they do, what would be the appropriate timing for treatment," Grafton-Cardwell said.  "If a broad spectrum pesticide is used, we need to know whether it will disrupt the citrus IPM program."  Grafton-Cardwell is conducting a study in Kern County near Edison, where 90 percent of the citrus orchards have some glassy-winged sharpshooters. She found that the pesticide Success has no effect on the pest.  The selective systemic pesticide Admire brings populations down, but not as well as the broad-spectrum sprays.  She will continue a monitoring program to document the effects of these treatments on citrus IPM programs.  For more information contact Beth Grafton-Cardwell at (559) 646-6591, bethgc@uckac.edu.

Glassy-winged sharpshooters' low flying pattern may protect farms

Glassy-winged sharpshooters' natural tendency to fly between about 3 and 16 feet from the ground may help farmers prevent the spread of diseases transmitted by the pest.  UC Riverside post-doctoral researcher Matthew Blua will this year begin a study to determine whether tall mesh fences erected between citrus orchards and vineyards will stop the glassy-winged sharpshooter in its tracks.  Last year, Blua placed sharpshooter traps on poles at about 3, 10, 16 and 23 feet from the ground.  "Ninety-five percent of glassy-winged sharpshooters were caught at five meters (about 16 feet) or lower," Blua said.  "We would like to take advantage of that potential weak link in the system to keep sharpshooters out of vineyards."  With funding from the City of Temucula and Riverside County, Blua will have a 26-foot-tall mesh fence built between citrus orchards and vineyards this summer.  "We want to know if the glassy-winged sharpshooter makes contact with the barrier, if they walk up, or fly up and over, or if they turn around and fly the other way," Blua said.  "We'll also be looking at the barrier combined with pesticide treatments to see what impact they have on preventing infection of grapevines with Pierce's disease."  For more information contact Matthew Blua, (909) 787-6301, matthew.blua@ucr.edu.

Vegetation management program under way in Napa and Sonoma to control blue-green sharpshooters

University researchers are now implementing vegetation management methods in Napa and Sonoma counties to control the blue-green sharpshooter, the main culprit behind Pierce's disease in coastal California.  Working under the auspices of the California Department of Fish and Game, the scientists have collaborated with environmental interest groups, grower groups and government agencies over the past five years to devise a strategy in accordance with existing environmental regulations. The program involves removing plants attractive to the blue-green sharpshooter during its egg-laying period - generally five or six plant species in any given riparian habitat. "If conducted properly, the vegetation management approach to controlling the blue-green sharpshooter is a 'win-win' situation for both the riparian environment and grape growers threatened by Pierce's disease near riparian areas," says Alexander Purcell, a UC Berkeley professor of entomology and one of the world's leading experts on insect vectors of Pierce's disease.  "In general, vegetation management methods increase biodiversity of plants and hopefully will reduce or eliminate the need for insecticide applications."  The researchers are conducting workshops to train growers and vineyard workers in the objectives and methods of the vegetation management program. For more information contact Alexander Purcell at (510) 642-7285, purcell@nature.berkeley.edu. Tip by Jill Goetz, (510) 643-1042, jgoetz@nature.berkeley.edu.

Pierce's disease bacteria are likely to be in most California counties

The bacterium that causes Pierce's disease in grapes, Xylella fastidiosa, is probably in every county in the state of California where grapes are grown, according to UC Davis plant pathologist Bruce Kirkpatrick.  "The bacteria have such a wide plant host range - in agricultural crops, ornamental plants, riparian plants and many common weeds - I'm certain there are plants infected with the bacteria in nearly every part of the state," Kirkpatrick said.  The bacteria can be transmitted by xylem-feeding insects including the smoke tree sharpshooter, the blue-green sharpshooter and the newly introduced glassy-winged sharpshooter.  The strain of bacteria that causes Pierce's disease in grapes also causes almond leaf scorch in almonds and alfalfa dwarf disease in alfalfa.  These latter two diseases have been comparatively rare in California.  A different strain of Xylella fastidiosa, also found in California, causes oleander leaf scorch disease in oleander shrubs.  Currently, several other very harmful strains of the bacteria are not present in California.  One causes phony peach disease and plum leaf scald in the southeastern part of the United States.  Another strain, found only in Brazil, causes citrus variegated chlorosis.  The Brazilian strain appeared mysteriously there 10 to 15 years ago.  "How it evolved or how it got there, no one knows," Kirkpatrick said.  However, if the strain makes its way to California, the disease will be devastating to citrus growers.  For more information contact Bruce Kirkpatrick at (530) 752-2831, bckirkpatrick@ucdavis.edu.

Sharpshooters appear to be well-established in Fresno area

Several glassy-winged sharpshooter egg masses collected in southeast Fresno backyards have produced parasites, according to Richard Coviello, entomology farm advisor for UC Cooperative Extension in Fresno County.  The birth of parasites, Coviello said, reveals good news and bad news.  The good news is that natural enemies of the glassy-winged sharpshooter are helping to keep their numbers down.  The bad news is the parasites indicate the pest has probably been in the vicinity for more than a year and is too well established to be susceptible to eradication.  The insects that emerged from the Fresno sharpshooter egg masses were Gonatocerus ashmeadi, parasitoids found in all areas where glassy-winged sharpshooters are established.  "Since glassy-winged sharpshooters appear to be established here, the best long-term hope for living with them is research," Coviello said.  For more information contact Richard Coviello at (559) 456-7549, rlcoviello@ucdavis.edu.

Oleander leaf scorch readily transmitted by glassy-winged sharpshooter

Another emerging sign of glassy-winged sharpshooter's ubiquitous presence in Southern California is oleanders dying along roads and in landscapes.  The drought-tolerant, hardy evergreen shrub is falling victim to a strain of the bacteria Xylella fastidiosa that causes oleander leaf scorch, a disease that begins with yellow margins or spots on the leaves before the edges and tips take on a scorched appearance.   Typically, within two years the plant wilts and dies.  Estimates indicate that CalTrans alone stands to suffer at least a $52 million loss if they are forced to replace the more than 2,000 miles of oleander freeway plantings.  UC Riverside entomologist Heather Costa has found in greenhouse experiments that glassy-winged sharpshooters transmit the disease efficiently.   Exposed to just one insect for five days, 83% of the plants were infected with the disease.  One year after contracting the disease from glassy-winged sharpshooters, more than half of the "Hardy Pink" and "Hardy Red" varieties of oleanders had died.  However, none of the "Ruby Lace" variety died.  "This indicates that some oleander varieties may have a degree of natural tolerance for the disease," Costa said.  For more information contact Heather Costa at (909) 787-4737, heather.costa@ucr.edu.

For more information on the glassy-winged sharpshooter and Pierce's disease, go to the UC Ag and Natural Resources media kit on those subjects at http://danr.ucop.edu/news/mediakit/gwss.shtml.