FOR IMMEDIATE RELEASE: November 21, 2005
CONTACT: Janet Byron, (510) 987-0668 or janet.byron@ucop.edu

October-December 2005 California Agriculture magazine

MEDIA ADVISORY
California Agriculture special focus:
Testing times follow two cases of mad cow disease

Also in this issue:

• When parasites kill pests: Two innovative “biocontrol” programs are lowering glassy-winged sharpshooter and eucalyptus-feeding psyllid populations
• Managed grazing and seedling shelters enhance oak regeneration on rangelands

While only two cases of mad cow disease (bovine spongiform encephalopathy, or BSE) have been confirmed in the United States since late 2003, they set off a national debate over how and to what degree American cattle should be tested for BSE. The current issue of the University of California’s peer-reviewed California Agriculture journal focuses on the policy implications of the U.S. cases of the fatal bovine disease.
“Critical questions facing the U.S. policy establishment include which tests to use, how many cattle to test, which cows to test, whether to decentralize testing sites, and in particular, whether or not to allow testing on farms,” writes Kate O’Neill, associate professor in the UC Berkeley Department of Environmental Science, Policy and Management, in the October-December 2005 issue.
In peer-reviewed studies, O’Neill analyzes U.S. regulatory policies regarding testing cattle for BSE, while UC Davis researchers describe a new DNA-based test to detect bovine contamination of cattle feed. In an editorial overview, leaders of the UC Davis School of Veterinary Medicine, Bennie Osburn (dean) and Donald Klingborg (associate dean), discuss how University of California scientists are contributing to efforts to better understand, monitor and control BSE. Related news coverage explores recent BSE-related policy and research.
BSE is spread among cattle via feed contaminated with rendered ruminant animals infected by similar diseases. This practice was widespread in the United Kingdom — where BSE devastated the cattle industry during the 1990s — but is less common in the United States. BSE has been identified in cattle from about two-dozen nations around the world, albeit at much lower levels than those found in the United Kingdom. Scientists linked consumption of BSE-infected beef to variant Creutzfeldt-Jakob disease, a new form of an extremely rare but fatal brain disease in humans.
In 2004, the USDA vastly expanded BSE testing rates, with the majority of the program voluntary. To date the USDA has tested nearly 500,000 cattle for BSE. Critics of the current testing policy note that about 36 million cattle are slaughtered in the United States each year, making current levels insufficient. They also have called for disclosure of geographic location, age and disease status of sampled cattle. But proponents argue that the low levels of BSE found in the United States do not warrant the huge expense of a significantly expanded testing program.

When parasites kill pests: Two innovative “biocontrol” programs are lowering glassy-winged sharpshooter and eucalyptus-feeding psyllid populations
Without any natural enemies to keep them in check, nonnative pest insects often have a field day feeding on California crops and plants. In California, populations of two such pests — the glassy-winged sharpshooter, which threatens the state’s valuable grape industry, and the red gum lerp psyllid, which attacks eucalyptus trees — are in retreat after UC researchers identified, tested, bred and released natural parasites of the pest insects.
In two peer-reviewed studies published in the October-December 2005 issue of the University of California’s California Agriculture research journal, UC scientists describe their efforts to establish natural enemies of these major pests by attacking them without the use of insecticides. Rather, they employed “biological control,” which involves introducing natural pests or parasites of the pest insect.
The glassy-winged sharpshooter invaded California around 1990. The one-half-inch insect is a vector of Xylella fastidiosa, a bacterium that causes Pierce’s disease in grapevines as well as other plant maladies such as leaf scorch in oleander and liquidambar in olive trees. Researchers from UC Riverside, the U.S. Department of Agriculture’s Agricultural Research Service, and the California Department of Food and Agriculture imported four parasitic wasps from the southeastern United States — the glassy-winged sharpshooter’s original home.
The tiny wasps parasitize the sharpshooters’ egg masses, preventing it from reproducing. More than 1.2 million parasitoids have been released at 373 sites in 13 California counties where the sharpshooter has been found.
The parasitic wasps are slowly establishing stable populations, says Leigh Pilkington of UC Riverside, lead author of the study. “Biological control with host-specific parasitoids may be the only feasible control strategy for providing long-term, area-wide suppression of the glassy-winged sharpshooter in areas where the climate is favorable to establishment.”
The red gum lerp psyllid preys on eucalyptus trees, both of which are native to Australia. The red gum lerp psyllid became established in California in the late 1990s and has caused considerable damage to eucalyptus trees around the state. To control the psyllid, UC researchers traveled to Australia and found a natural pest of the psyllid — a parasitoid called Psyllaphaegus bliteus that lays its eggs inside the psyllid’s nymphs and prevents them from reaching maturity.
Nearly 50,000 P. bliteus parasitoids were released between 2000 and 2003 at 78 release sites in 42 California counties. Subsequent monitoring has found that the parasitoid is now well established in coastal areas, with concurrent declines in psyllid populations of between 78.6% and 44.8% depending on release location. However, psyllid densities have not declined significantly in some parts of the Central Valley, most likely due to climatic differences that affect the establishment of P. bliteus.
“The red gum lerp psyllid now appears to bein check in most coastal regions of California,” wrote UC Berkeley’s Kent Daane, lead author of the study. “As psyllid numbers have dropped, the defoliation and death of eucalyptus trees due to the psyllid have been reduced.”
The red gum lerp psyllid project is a tribute to the legacy of Donald Dahlsten, UC Berkeley professor of insect biology, who was a pioneer in the biological control of pest insects (http://www.berkeley.edu/news/media/releases/2003/09/10_Dahlsten.shtml). Dahlsten initiated and oversaw the psyllid project before his death in 2003. He is first author of the study published in California Agriculture, which was written by Daane.

Managed grazing and seedling shelters enhance oak regeneration on rangelands
For at least a century, scientists have been concerned that some of California’s 20 native oak species are not regenerating adequately, especially in the state’s 10 million acres of oak habitat that are grazed by cattle.
In the October-December 2005 issue of the University of California’s California Agriculture research journal, scientists with the UC Integrated Hardwood Range Management Program review two decades of research concerning the regeneration of oaks in California rangelands.
Douglas McCreary, natural resources specialist at the UC Sierra Foothill Research and Extension Center, and Mel George, rangeland management specialist at UC Davis, conclude that while “livestock grazing is a principal factor in poor oak regeneration in California,” land managers can promote oak regeneration by “physically protecting seedlings and managing stock densities and grazing seasons.”
The article reports on a series of studies in the Sierra foothills which showed that cattle will indeed graze on oak seedlings, in particular during times of the year when grass is less plentiful or when high densities of cattle are allowed to graze in a certain area. Other trials confirmed that excluding cattle from oak woodlands allows more oak seedlings to grow.
Further studies found that seedlings in grazed woodlands can survive and thrive if protected by simple, inexpensive tree shelters — rigid plastic tubes placed over individual seedlings. If seedlings are protected until they reach a threshold height of 6.5 feet, “oaks may [then] be large enough to withstand cattle damage in lightly to moderately grazed pastures and continue growing,” McCreary and George wrote.