SACRAMENTO — The California Department of Food and Agriculture (CDFA) and the United States Department of Agriculture (USDA) have established a 94-square mile quarantine in portions of Riverside and San Bernardino counties following the detection of the citrus disease huanglongbing (HLB), or citrus greening, in a single citrus tree in the city of Riverside. HLB is a deadly disease of citrus plants and closely related species, and can be transmitted from tree to tree by the Asian citrus psyllid.

The quarantine boundaries are on the north, Interstate 10; on the east, Box Springs Mountain Reserve; on the west, Riverside Municipal Airport; and on the south, East Alessandro Boulevard. HLB quarantine maps for Riverside and San Bernardino counties are available online at: www.cdfa.ca.gov/plant/pe/InteriorExclusion/hlb_quarantine.html. Please check this link for future quarantine expansions in these counties, should they occur.  Quarantines are already in place for HLB in portions of Los Angeles and Orange counties.

The quarantine will prohibit the movement of all citrus nursery stock out of the area, while maintaining existing provisions allowing the movement of only commercially cleaned and packed citrus fruit.  Any fruit that is not commercially cleaned and packed, including residential citrus, must not be removed from the property on which it is grown, although it may be processed and/or consumed on the premises.

Residents are urged to take several steps to help protect citrus trees:

• Do not move citrus plants, leaves or foliage into or out of the quarantine area, or across state or international borders.  Keep it local.
• Cooperate with agricultural crews placing traps, inspecting trees and treating for the pest.
• If you no longer wish to care for your citrus tree, consider removing it so it does not become a host to the pest and disease.

CDFA crews have already removed the infected tree and are in the midst of a treatment program for citrus trees to knock down Asian citrus psyllid infestations within 800 meters of the find site. By taking these steps, a critical reservoir of the disease and its vectors will be removed, which is essential to protect the surrounding citrus from this deadly disease.

HLB is a bacterial disease that attacks the vascular system of plants.  It does not pose a threat to humans or animals.  The Asian citrus psyllid can spread the bacteria as the pest feeds on citrus trees and other plants. Once a tree is infected, there is no cure; it typically declines and dies within a few years.

CDFA, in partnership with the USDA, local county agricultural commissioners and the citrus industry, continues to pursue a strategy of controlling the spread of the Asian citrus psyllids while researchers work to find a cure for the disease.

—California Department of Food and Agriculture

Over 20 new trees in Southern California have been confirmed HLB-positive. The new finds raise the total number of trees with huanglongbing disease found in California to around 100. All of the trees found in the state have been located in residential areas.

The Citrus Pest and Disease Prevention Program (CPDPP) issued a press release that stated 21 trees in Anaheim, and four trees in Pico Rivera tested HLB-positive. The CPDPP, a program of the California Department of Food and Agriculture (CDFA), stated the current quarantine in Southern California would be slightly expanded in Orange and Los Angeles Counties.

The new detections were found due to intensive surveying that's part of the response program. Highly trained crews sample trees where HLB-positive Asian citrus psyllids have been found. CDFA says their Sacramento facility can process 10,000 samples a month.

All of the detections in California have been residential trees. The CPDPP is currently running an outreach program that involves public service announcements, coordination with officials, and large public events in the quarantine area. The goal is to educate residents on the disease and the insect that spreads it. Go to the CPDPP website to find out more about the disease, insect, and quarantines.

Photo: HLB symptoms

It really has gotten out of hand - Hairy Fleabane and Horseweed which are both Conyza weed species that have run rampant this year because of the extra rain.  It's also because they have become resistant to glyphosate herbicide. The problem has shown up all over the US and other parts of the world.  Gradually as resistance has grown and their resistant fairy seeds have floated wherever the winds go, the weed is having a field day everywhere in your backyard, in your orchard, in the sidewalk.  It's not just abandoned areas, but in actively managed areas where Cal Trans is doing its best.

Citrus growers who have not used preemergents in years or never used them have turned to various cocktails to knock it out.

A good description of the biology and care of Conyza can be found at:

https://anrcatalog.ucanr.edu/pdf/8314.pdf

And we along with others have written about this problem in the past - 

http://ucanr.edu/blogs/topics/index.cfm tagname=Conyza , 

http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=10648 , 

http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=20061

But this year has been exceptional in the ubiquity of this plant. Something more than glyphosate is called for at this point. Glufosinate is a postemergent herbicide somewhat similar to glyphosate in name only and more expensive.  It is a broadspectrum herbicide that is effective with thorough coverage on younger stages of conyza and other weeds.  It will take some learning to get the best effect out of it.  Citrus growers have been able to use it for several years now and have enjoyed its effectiveness. We are currently working on an IR-4 registration (http://ir4.rutgers.edu/) for avocados. It is currently not registered for use in avocado.

Mature avocados are pretty good about controlling any weeds in their own orchards through ground shading and self mulching, but conyza has become a problem in young orchards.  And this new herbicide could help.

California citrus farmers have their ears perked for all news related to Asian citrus psyllid (ACP) and huanglongbing (HLB) disease, but the very latest advances have been available only in highly technical research journals, often by subscription only.

UC Cooperative Extension scientists are now translating the high science into readable summaries and posting them on a new website called Science for Citrus Health to inform farmers, the media and interested members of the public.

“The future of the California citrus depends on scientists finding a solution to this pest and disease before they destroy the industry,” said Beth Grafton-Cardwell, UC Cooperative Extension citrus entomology specialist. “Our farmers want to stay on top of all the efforts to stop this threat.”

The new 'Science for Citrus Health' website can be found at http://ucanr.edu/sites/scienceforcitrushealth/

Grafton-Cardwell and UC Cooperative Extension biotechnology specialist Peggy Lemaux are the two scientists behind the new website. When scientists make progress toward their goals, Grafton-Cardwell and Lemaux craft one-page summaries with graphics and pictures to provide readers with the basics.

For example, the website outlines scientific endeavors aimed at stopping the spread of huanglongbing disease by eliminating the psyllid's ability to transfer the bacterial infection. This section is titled NuPsyllid, and contains summaries of three research papers including one by UC Davis plant pathologist Bryce Falk.

Falk is collecting viruses found in Asian citrus psyllid; so far he has identified five. He is looking into the potential to utilize one of the viruses as is or modify one of the viruses to block the psyllid's ability to transmit the bacterium.  For example, the virus might out compete the bacterium in the psyllid's body.   

Another focus of the website is HLB early detection techniques (EDTs). If HLB-infected trees are found and destroyed before they show symptoms, ACP is less likely to spread the disease to other trees. EDT research described on the website includes efforts to detect subtle changes in the tree that take place soon after infection, such as alterations in the scents that waft from the tree (studied by UC Davis engineer Cristina Davis), changes in the proteins in the tree (studied by UC Davis food scientist Carolyn Slupsky) and starch accumulation in the leaves (studied by UC farm advisor Ali Pourreza).

Other research areas on the Science for Citrus Health website are solutions for established orchardsand replants.

As more research is published, more one-page descriptions will be added to the website. The website contains a feedback form to comment on the science and the summaries.

Photo:  ACP traps

Two more trees infected with huanglongbing (HLB) disease were identified and destroyed in the days before UC Cooperative Extension and the Citrus Research Board kicked off their spring Citrus Growers Education Seminar in Exeter June 27. The new infections raise the total number of HLB-infected trees in Los Angeles and Orange counties to 73.

The latest statistic set the stage for spirited discussions about a looming threat that cut Florida citrus production by 60 percent in 15 years. The devastating citrus losses in Florida were recounted by Ed Stover, a plant breeder with USDA Agricultural Research Service in Fort Pierce. 

An abandoned orange grove in Florida. (Photo: USDA)

"One of the benefits of coming here is I am reminded how beautiful citrus is," Stover said. "In Florida, there are more than 130,000 acres of abandoned groves." He showed slides of trees with thin canopies, pale leaves and green fruit; in one image the trees were skeletons among tall weeds.

Huanglongbing disease is an incurable condition spread by Asian citrus psyllid (ACP). The psyllid, native of Pakistan, Afghanistan and other Asian regions, was first detected in California in 2008. Everywhere ACP is found, the pests find and spread HLB.

Stover and his colleagues are searching for citrus cultivars that have natural tolerance for the bacteria that causes HLB, but progress is slow. Transgenic citrus, he said, is the best bet for developing citrus with HLB immunity.

"In my opinion, commercial genetically engineered citrus is inevitable, and GE crop concerns will likely decline with time," he said. 

In California, the aggressive push to keep psyllid populations low, regulations to limit the spread of psyllids when trucking the fruit, and active scouting for and removal of HLB infected trees in residential areas could buy time for researchers to find a solution before California suffers the fate of Florida citrus growers.

"Be vigilant," Stover said. "As long as you are still making a good return, there is almost no investment too great if it keeps HLB out of California."

UCCE specialist Beth Grafton-Cardwell outlines research underway to detect huanglongbing disease of citrus.

Beth Grafton-Cardwell, UCCE citrus entomology specialist and director of the UC Lindcove Research and Extension Center near Exeter, said the prime research in the San Joaquin Valley is aimed at early detection techniques.

Once a tree is infected, it takes nine months to two years for the bacteria to spread throughout the tree, so that when leaves are selected for testing, they detect the bacteria. Capturing and testing psyllids is one way to to find the disease early. Other early detection techniques focus on the microbes, proteins and aromas produced by sick trees.

"These can be measured with leaf test, a VOC (volatile organic compound) sniffer, swab or even dogs," Grafton-Cardwell said. "Scientists are studying every conceivable way to stop the disease."

In the meantime, growers were encouraged to carefully monitor for and treat psyllid populations in their orchards with pesticides. Pesticide treatment recommendations are available on Grafton-Cardwell's Asian Citrus Psyllid Distribution and Management website, http://ucanr.edu/acp.

"We have lots of challenges," Grafton-Cardwell conceded. "We hate disrupting our beautiful integrated pest management program. But monitor your own groves, apply the most effective treatments and remove suspected (infected) trees. Going through the pain up front will save us in the long run."