The site’s launch coincides with the announcement last month by the California Department of Food and Agriculture that six more psyllids were found in three Tulare County yellow sticky traps. In 2012, three psyllids were found on two traps and an eradication program ensued.
The new website was developed by Beth Grafton-Cardwell and Matt Daugherty, UCCE specialists in the Department of Entomology at UC Riverside, Karen Jetter, economist with the UC Agricultural Issues Center, and Robert Johnson programmer with the UC Agriculture and Natural Resources Informatics and GIS Statewide Program program. Funding for the site was provided by UC Agriculture and Natural Resources.
The website includes information on the psyllid's distribution in California, monitoring methods and treatment options. For example, the website suggests citrus farmers and homeowners not rely on yellow stick card traps to monitor for the pest.
“At certain times of the year, the yellow sticky cards are totally unattractive to Asian citrus psyllid,” Grafton-Cardwell said. “The cards are just color, but citrus flush is an attractive color and also emits irresistible volatiles or smells.”
The website advises farmers to regularly conduct systematic visual surveys along the margins of their orchards looking carefully at new green shoots and conducting tap sampling. To tap sample, spray a plastic surface with soapy water, position the plastic sheet underneath a branch and tap the branch above to dislodge adult ACP. The insects will stick to the filmy plastic where they can be studied with a magnifying hand lens to determine if they are psyllids.
If psyllids are found, the UC website outlines the immediate action that is required.
Adult psyllids should be placed in a container with 90 percent alcohol and reported to the county agricultural commissioner’s office so the insects can be tested for huanglongbing disease. Immature stages of the pest should be left on the tree so the ag commissioner’s office can make an official regulatory collection.
“Florida and Texas don’t have exactly the same insecticides that are available in California and the environmental conditions are different,” Grafton-Cardwell said. “Over time we will compare different treatments and determine how long they will protect the trees. Any new developments will be posted to the website.”
Because the goal in the San Joaquin Valley is eradication, Grafton-Cardwell recommends aggressive action against a psyllid infestation.
“The best approach is using two broad-spectrum insecticides within a short period of time,” she said. “No one insecticide will kill all the stages of the pest."
Another key to successful eradication is area-wide treatment coordination. Grafton-Cardwell suggests farmers work closely with their treatment liaisons and treat their orchards in a coordinated manner.
“The bigger the area being sprayed at the same time, the better,” Grafton Cardwell said. “If we get a blanket effect over the whole area, that’s been shown in Florida and Texas to have the greatest impact on the psyllid populations.”
The aggressive psyllid treatment aims to buy time for researchers to find long-term strategies for maintaining the California citrus industry in the presence of ACP and, especially, with the incurable and fatal citrus disease they spread, huanglongbing.
The July ACP find prompted the California Department of Food and Agriculture to quarantine 178 square miles in the Porterville area, placing severe restrictions on the movement of local citrus nursery stock and citrus fruit outside the area. It also prompted several hundred farmers and pest control advisers to gather July 30 at the International Agri-Center in Tulare for an update on the threat.
Like a scene from the film “Scared Straight,” Ken Keck, former executive director of the Florida Department of Citrus and now director of the California Citrus Research Board, admonished the California farmers to learn from the Sunshine State’s mistakes.
“I feel like the ex-con in front of a room of 17-year-olds,” Keck said. “All I can say is, ‘prevent, prevent, prevent.’”
Asian citrus psyllid is established in Southern California. Efforts in the southern part of the state are focused on managing the psyllids to reduce the likelihood they will find a tree infected with huanglongbing. Huanglongbing (HLB) is an incurable and fatal disease of citrus spread by ACP.
By working together and following science-based treatment strategies, UC Cooperative Extension specialist Beth Grafton-Cardwell believes farmers and CDFA can still eliminate ACP in the San Joaquin Valley, where the bulk of the state’s commercial citrus is grown.
At the Tulare meeting, Grafton-Cardwell explained the eradication strategy she developed by studying Asian citrus psyllid and huanglongbing disease management programs in Florida and Texas, another state where the pest is well established.
“We want to slow the spread of psyllid into new areas,” Grafton-Cardwell said. “We want to prevent psyllids from finding HLB infected trees.”
Although it is unlikely the pest and disease can be kept at bay indefinitely, Grafton-Cardwell said the battle will buy time for researchers to discover long-term approaches for maintaining California’s citrus industry in the presence of ACP and HLB.
Developing citrus varieties resistant to HLB through traditional breeding or genetic modification will take too long, she said. Scientists are considering such futuristic solutions as inserting HLB resistance into a mild form of the Tristeza virus and inoculating trees with the virus to fight HLB.
“Everyone is racing to come up with tactics to fight ACP and HLB,” she said. “I believe we will eventually be using multiple approaches, such as a repellent spray to keep ACP off the trees and perhaps breeding ACP that can’t transmit HLB and then flooding the population with these incapacitated psyllids.”
To fight ACP and HLB, growers and homeowners can access detailed information on the pest’s distribution, monitoring methods and treatment options on a new website created by Grafton-Cardwell with funding from UC Agriculture and Natural Resources.
For tap sampling, spray a plastic surface with
The website advises farmers and homeowners to regularly conduct visual surveys and tap sampling (see video on right) in their orchards. “Yellow sticky card traps are not very attractive to psyllids,” it says.
If psyllids are found, immediate action is required.
Adult psyllids should be placed in a container with 90% alcohol and reported to the county agricultural commissioner’s office so the insect can be tested for HLB. Immature stages of the pest should be left on the tree so the ag commissioner’s office can make an official regulatory collection.
An ACP find should also trigger rapid and wide treatment with the most effective pesticides possible.
Hailing Jin, an associate professor of plant pathology and microbiology at the University of California, Riverside, recently published a paper in the journal Molecular Plant in which she reports having profiled small ribonucleic acid (sRNA) from citrus plants, some of which were affected by HLB.
Her research showed that several sRNAs were found to have been induced specifically by HLB, meaning they could potentially be developed into early diagnosis markers for the disease.
The study also showed that in a three-year field trial in southwest Florida diseased trees suffered from severe phosphorus deficiency and that application of phosphorus solutions to the diseased trees significantly alleviated HLB symptoms, improving fruit yield.
In the trial, 19 healthy sweet orange trees were grafted with HLB-positive bark or leaf pieces. As controls, five trees were mock-inoculated with pathogen-free healthy tissue. Phosphorus solutions were applied to the 19 HLB-positive trees three times a year. After two years of treatment, the diseased trees displayed significantly reduced HLB symptoms.
“Compared with the mock-treated plants, the phosphorus-treated trees had a greener appearance and more vigorous growth,” Jin said. “Fruit yield increased approximately two-fold compared with the mock-treated plants.”
She cautioned that the application of phosphorus solutions did not cure the trees. Her research suggests, however, that additional phosphorus application may help diseased trees look healthier and improve fruit yield.
Jin was joined in the research by Hongwei Zhao, Ruobai Sun, Chellappan Padmanabhan, Airong Wang, Michael D. Coffey, Thomas Girke, Timothy J. Close, Mikeal Roose and Georgios Vidalakis at UC Riverside; and researchers at Nanjing Agricultural University, China; the U.S. Department of Agriculture; Fujian Agriculture and Forestry University, China; and the University of Florida.
The research was supported by a grant to Jin from California Citrus Research Board./span>/span>
“HLB is not just bad for growers and for the economy,” said Slupsky. “The loss of fresh oranges and other citrus could seriously impact our health.”
HLB is a disease caused by a microbe called Candidatus Liberibacter asiaticus and spread by the Asian citrus psyllid, a tiny insect that feeds on the leaves and stems of citrus trees. There is no cure yet for HLB, so once a tree is infected, it will slowly die. The disease has decimated citrus groves in Asia, Brazil and the Dominican Republic. Florida has lost one-third of its citrus to the disease. Both HLB and the Asian citrus psyllid have recently been spotted in California.
HLB is a silent killer – an infected tree can live for years without symptoms, allowing the pathogen to spread undetected to other trees. Symptoms emerge over time, as a tree’s fruit starts to turn green and misshapen, with a bitter, metallic taste.
Is there a way to spot HLB before visual symptoms occur? The microbe that causes HLB can sometimes be found in a leaf sample, but since the pathogen isn’t evenly distributed throughout the tree, results can be misleading.
“Just because the pathogen doesn’t show up in one leaf, that doesn’t guarantee the tree isn’t infected,” said MaryLou Polek, vice president of science and technology for the California Citrus Research Board. “So when you sample a leaf, there’s a high probability of a false negative result.”
Slupsky and Andrew Breksa, research chemist with the USDA Agricultural Research Service based in Albany, Calif., tried a different tack, searching for clues in a tree’s chemical fingerprint. They used nuclear magnetic resonance spectroscopy to study the amino acid composition of juice from three types of citrus: fruit from healthy tress, symptom-free (asymptomatic) fruit from HLB-positive trees, and fruit with symptoms from HLB-positive trees.
“We found major differences in the chemical fingerprint among healthy, asymptomatic and symptomatic fruits,” Slupsky said.
With further research, the profiles may prove to be a reliable, rapid, and early indicator of the presence of the HLB pathogen. With early detection, growers and regulators can know which trees might need to be removed before the disease spreads throughout the orchard (and beyond).
“These findings are huge for citrus growers, backyard gardeners and everyone who loves fresh citrus,” Polek said.
And there’s more. While analyzing the amino acids, Slupsky and Breksa discovered what looks like a mechanism underlying the microbe’s mode of attack.
“The pathogen responsible for HLB seems to cause havoc with a tree’s ability to defend itself from infection,” Slupsky said.
Trees need amino acids for growth, development and defense. From Slupsky and Breksa’s studies, it looks like the HLB pathogen affects the trees’ ability to create, use and recycle some of those amino acids. For example, a tree can convert the amino acid phenylalanine into cinnamic acid, a precursor to compounds important to the tree’s defense systems. But juice from oranges of HLB-positive trees had significantly higher concentrations of phenylalanine. Also, juice from oranges grown on HLB-infected trees contained a lot less of the amino acid proline, which a tree usually synthesizes when it knows something is wrong.
“It could be that the pathogen is outsmarting the tree by undermining its defenses,” Slupsky said. “That’s a spectacular discovery, because when we understand the mechanisms behind the attack, we have a chance at blocking them. Maybe we can find ways to enhance a tree’s natural immunity.”
As tough as HLB has been on citrus in Florida, the stakes are even higher in California where so much of the world’s fresh citrus is produced.
“Florida’s citrus industry produces mostly orange juice, and they can use additives and filtration to adjust for the bitter taste of HLB-affected fruit,” Polek said. “It can be reduced to sugar water, essentially, and then built back up to taste like orange juice. We produce fresh citrus here in California, and chemistry is not an option.”
Losing fresh citrus is a real possibility if HLB spreads throughout California, and that prospect is the driving force behind Slupsky’s research.
“From a nutritional standpoint, it’s hard to beat the importance of fresh citrus,” Slupsky said. “Oranges provide energy, pectin, and a wide variety of nutrients, vitamins and minerals. They’re one of the most consumed fruits in the United States. I can’t imagine life without fresh citrus.”
Slupsky and Breksa collaborated with Thomas G. McCollum of the ARS Horticultural Research Laboratory in Fort Pierce, Florida, along with Anne Slisz and Darya Mishchuk of Slupsky’s lab. A peer-reviewed article on their findings was published in the Journal of Proteome Research in June 2012. You can access the article at http://pubs.acs.org/doi/abs/10.1021/pr300350x.
Tamarixia radiata – tiny, stingless parasitic wasps that lay eggs in Asian citrus psyllid nymphs – were released in a citrus grove behind the residence of UC Riverside Chancellor Tim White. Over the next several years, UC Riverside and California Department of Food and Agriculture scientists will raise thousands of Tamarixia for release throughout California. The Tamarixia larvae will eat the ACP nymphs, killing them, and emerge as adults about 12 days later. Adult female Tamarixia also eat other ACP nymphs, killing many this way as well.
On Dec. 7, 2011, state and federal authorities cleared Tamarixia from quarantine with the issuance of a permit to release this natural enemy for establishment in California. The parasitic wasps can’t bite or sting people or animals. Safety testing in quarantine has demonstrated that the parasites are disease free and pose no environmental risk.
The Indian subcontinent is likely part of the native range for Asian citrus psyllid, Hoddle said. The first study of the pest was published in 1927 by scientists in the region. Asian citrus psyllid is now found in parts of the Middle East, South and Central America, Mexico and the Caribbean. In the United States, this psyllid was first detected in Florida in 1998 and is now also found in Louisiana, Georgia, South Carolina, Texas and Arizona. In 2008, the pest was detected for the first time in California in San Diego and Imperial county backyard trees. Large populations of Asian citrus psyllid are now well established in urban areas of Los Angeles, San Bernardino and Riverside counties.
Huanglongbing has made its way to Mexico and Florida, but so far it has not been detected in California. Currently, the citrus industry is dependent on insecticide sprays to control ACP and prevent the introduction of Huanglongbing. UC Cooperative Extension citrus entomology specialist Beth Grafton-Cardwell, director of the UC Lindcove Research and Extension Center, welcomes the promise of biological control with introduced natural enemies.
“This is very good news for the integrated management of Asian citrus psyllid and a highly significant contribution of the University of California,” Grafton-Cardwell said. “Parasitoid releases will add a new and exciting component to the management program for ACP, especially for the many homeowners who have citrus trees in their yards.”
Hoddle said Tamarixia won’t eradicate Asian citrus psyllid, but scientists predict it will reduce the densities of the pest, giving other control practices a better chance of working. Commercial citrus producers in California will still need to apply insecticides to control Asian citrus psyllid and prevent the spread of Huanglongbing, should it be found in the state. However, the frequency of these applications may be reduced because Tamarixia is killing ACP nymphs in areas that are not sprayed.
Hoddle collected the parasites in collaboration with scientists in the Department of Agri-Entomology at the University of Agriculture in Faisalabad (UAF), Pakistan. UAF was an ideal base for the project, Hoddle said, because it had citrus research plots infested with Asian citrus psyllid that have not been treated with insecticides. The university is also situated near local commercial citrus production, the area has a climate similar to citrus-growing regions of California, and the university’s vice chancellor, Iqrar Khan, is a UC Riverside graduate who also has an active research program on Huanglongbing in Pakistan.
In March and April 2011, Hoddle spent four weeks at UAF to set up research plots in kinnow and sweet orange trees. Coincidentally, kinnow is a mandarin that was bred at UC Riverside in 1935 and accounts for 85 percent of citrus produced in the Punjab. Hoddle and his Pakistani colleagues collected 24 male and 56 female Tamarixia radiata, which were brought back to UC Riverside to establish colonies.
Hoddle returned from a June 2011 trip to Pakistan with 151 male and 255 female Tamarixia radiata. An October and November 2011 visit netted another 800 parasitic wasps.
“Gathering insects from citrus plants in the Punjab generated an immense amount of curiosity,” Hoddle said. “Kids in particular were super-curious about what we were doing, where we had come from and why we had come to Pakistan. The people in the Punjab were incredibly courteous, polite and generous.”
Hoddle has trained a Pakistani graduate student Shouket Zaman Khan at UAF to monitor the interaction of Asian citrus psyllid with its natural enemies in their native environment. The researchers will determine whether other natural enemies of the pest could provide additional biological control of California ACP in the future.
Funding for the Asian citrus psyllid biocontrol effort has been provided by the California Department of Agriculture Food and Agriculture Specialty Crops Program, the USDA Citrus Health Response Program, the Citrus Research Board, and the UC Hansen Trust.
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MEDIA CONTACT: Mark Hoddle, UC Cooperative Extension biological control specialist based at UC Riverside, (951) 827-4714, firstname.lastname@example.org/table>/div>