- Author: Olga Kuchment, Communications Specialist, Texas A&M AgriLife
- Author: Mike Hsu
UC ANR part of team led by Texas A&M AgriLife combating huanglongbing disease
Citrus greening, or huanglongbing disease (HLB), is the most devastating disease for orange and grapefruit trees in the U.S. Prevention and treatment methods have proven elusive, and a definitive cure does not exist.
Since HLB was detected in Florida in 2005, Florida's citrus production has fallen by 80%. Although there have been no HLB positive trees detected in commercial groves in California, more than 2,700 HLB positive trees have been detected on residential properties in the greater Los Angeles region.
“It is likely only a matter of time when the disease will spread to commercial fields, so our strategy in California is to try to eradicate the insect vector of the disease, Asian citrus psyllid,” said Greg Douhan, University of California Cooperative Extension citrus advisor for Tulare, Fresno and Madera counties.
Now, a public-private collaborative effort across Texas, California, Florida and Indiana will draw on prior successes in research and innovation to advance new, environmentally friendly and commercially viable control strategies for huanglongbing.
Led by scientists from Texas A&M AgriLife Research, the team includes three UC Agriculture and Natural Resources experts: Douhan; Sonia Rios, UCCE subtropical horticulture advisor for Riverside and San Diego counties; and Ben Faber, UCCE advisor for Ventura, Santa Barbara and San Luis Obispo counties.
$7 million USDA project
The $7 million, four-year AgriLife Research project is part of an $11 million suite of grants from the U.S. Department of Agriculture National Institute of Food and Agriculture, NIFA, to combat HLB. The coordinated agricultural project is also a NIFA Center of Excellence.
“Through multistate, interdisciplinary collaborations among universities, regulatory affairs consultants, state and federal agencies, and the citrus industry, we will pursue advanced testing and commercialization of promising therapies and extend outcomes to stakeholders,” said lead investigator Kranthi Mandadi, an AgriLife Research scientist at Weslaco and associate professor in the Department of Plant Pathology and Microbiology at the Texas A&M College of Agriculture and Life Sciences.
The UC ANR members of this collaboration will be responsible for sharing findings from the research with local citrus growers across Southern California, the desert region, the coastal region and the San Joaquin Valley.
“In addition to the ground-breaking research that will be taking place, this project will also help us continue to generate awareness and outreach and share the advancements taking place in the research that is currently being done to help protect California's citrus industry,” said Rios, the project's lead principal investigator in California.
Other institutions on the team include Texas A&M University-Kingsville Citrus Center, University of Florida, Southern Gardens Citrus, Purdue University and USDA Agricultural Research Service.
“This collaboration is an inspiring example of how research, industry, extension and outreach can create solutions that benefit everyone,” said Patrick J. Stover, vice chancellor of Texas A&M AgriLife, dean of the Texas A&M College of Agriculture and Life Sciences and director of Texas A&M AgriLife Research.
HLB solutions must overcome known challenges
An effective HLB treatment must avoid numerous pitfalls, Mandadi explained.
One major problem is getting a treatment to the infected inner parts of the tree. The disease-causing bacteria only infect a network of cells called the phloem, which distributes nutrients throughout a tree. Starved of nutrients, infected trees bear low-quality fruits and have shortened lifespans.
Treatments must reach the phloem to kill the bacteria. So, spraying treatments on leaves has little chance of success because citrus leaves' waxy coating usually prevents the treatments from penetrating.
Second, while the bacteria thrive in phloem, they do not grow in a petri dish. Until recently, scientists wishing to test treatments could only do so in living trees, in a slow and laborious process.
Third, orange and grapefruit trees are quite susceptible to the disease-causing bacteria and do not build immunity on their own. Strict quarantines are in place. Treatments must be tested in groves that are already infected.
Two types of potential HLB therapies will be tested using novel technologies
The teams will be working to advance two main types of treatment, employing technologies they've developed in the past to overcome the problems mentioned above.
First, a few years ago, Mandadi and his colleagues discovered a way to propagate the HLB-causing bacteria in the lab. This method involves growing the bacteria in tiny, root-like structures developed from infected trees. The team will use this so-called “hairy roots” method to screen treatments much faster than would be possible in citrus trees.
“Even though a particular peptide may have efficacy in the lab, we won't know if it will be expressed in sufficient levels in a tree and for enough time to kill the bacteria,” Mandadi said. “Viruses are smart, and sometimes they throw the peptide out. Field trials are crucial.”
The second type of treatment to undergo testing is synthetic or naturally occurring small molecules that may kill HLB-causing bacteria. Again, Mandadi's team will screen the molecules in hairy roots. A multistate team will further test the efficacy of the most promising molecules by injecting them into trunks of infected trees in the field.
A feasible HLB treatment is effective and profitable
Another hurdle to overcome is ensuring that growers and consumers accept the products the team develops.
“We have to convince producers that the use of therapies is profitable and consumers that the fruit from treated trees would be safe to eat,” Mandadi said.
Therefore, a multistate economics and marketing team will conduct studies to determine the extent of economic benefits to citrus growers. In addition, a multistate extension and outreach team will use diverse outlets to disseminate project information to stakeholders. This team will also survey growers to gauge how likely they are to try the treatments.
“The research team will be informed by those surveys,” Mandadi said. “We will also engage a project advisory board of representatives from academia, universities, state and federal agencies, industry, and growers. While we are doing the science, the advisory board will provide guidance on both the technical and practical aspects of the project.”
Project team members:
—Kranthi Mandadi, Texas A&M AgriLife Research.
—Mike Irey, Southern Gardens Citrus, Florida.
—Choaa El-Mohtar, University of Florida Institute of Food and Agricultural Sciences, Citrus Research and Education Center.
—Ray Yokomi, USDA-Agricultural Research Service, Parlier, California.
—Ute Albrecht, University of Florida IFAS Southwest Florida Research and Education Center.
—Veronica Ancona, Texas A&M University-Kingsville Citrus Center.
—Freddy Ibanez-Carrasco, Texas A&M AgriLife Research, Department of Entomology, Weslaco.
—Sonia Irigoyen, AgriLife Research, Texas A&M AgriLife Research and Extension Center at Weslaco.
—Ariel Singerman, University of Florida IFAS Citrus Research and Education Center.
—Jinha Jung, Purdue University, Indiana.
—Juan Enciso, Texas A&M AgriLife Research, Department of Biological and Agricultural Engineering, Weslaco.
—Samuel Zapata, Texas A&M AgriLife Extension, Department of Agricultural Economics, Weslaco.
—Olufemi Alabi, Texas A&M AgriLife Extension, Department of Plant Pathology and Microbiology, Weslaco.
—Sonia Rios, University of California Cooperative Extension, Riverside and San Diego counties.
—Ben Faber, University of California Cooperative Extension, Ventura, Santa Barbara and San Luis Obispo counties.
—Greg Douhan, University of California Cooperative Extension, Tulare, Fresno and Madera counties.
- Author: Jeanette Alosi
By Jeanette Alosi, UC Master Gardener of Butte County, May 3, 2019
Butte County is known for its delicious citrus. Mandarins are grown commercially in our “banana belt” foothills, and residents in the valley can enjoy citrus grown in their own gardens. However, a tiny flying insect the size of an aphid poses a grave threat to our local citrus. This insect is the Asian citrus psyllid (ACP), a vector for a dangerous and fatal bacterium (Candidatus Liberibacter asiaticus) that causes Huanglongbing (HLB) disease, previously known as Citrus Greening disease. HLB has devastated the Florida citrus industry and has been found in Southern California. Recently the Asian citrus psyllid itself (but not HLB) was found in Sacramento, just 100 miles south.
ACP was first detected in Southern California in 2008, followed by HLB detection in 2012. The psyllid has expanded into the Central Valley, the Central Coast and as far north as the Bay Area and Sacramento. So far there has been no detection of HLB disease outside of Southern California.
There is no cure for HLB, which can kill a tree in 5 to 8 years. Because HLB can only be spread via the ACP, the key to prevent HLB is monitoring for, and controlling, the psyllid.
Adults only live for a few months but can lay several hundred tiny, yellow-orange, almond-shaped eggs in fresh new citrus growth. The tiny wingless nymphs hatch from the eggs and are yellow, orange or brown. They molt 4 times, increasing in size each time.
ACP nymphs only feed on new citrus shoots and leaves. As they feed, a toxin is injected causing leaves to twist and curl, sometimes killing new shoots. Nymphs also produce excess sap or honeydew which promotes the growth of sooty mold. To direct the honeydew away from their bodies, they produce waxy, white tubules. The tubules are unique to the nymphs and are easily identified. Other insects such as aphids can cause these same symptoms, but they do not produce tubules nor are they a vector for the bacterium causing HLB.
Now that the ACP is firmly established in California, the Department of Food and Agriculture (CDFA) is tracking its distribution through the use of yellow sticky traps in commercial and residential areas. ACP quarantine zones are being used to restrict the transport of citrus trees and the spread of the psyllid. Biological controls using predators and parasites that feed on the ACP are being used to help control (but not eradicate) the ACP.
The University of California Division of Agricultural and Natural Resources has an updated map on the spread of the ACP and HLB you can find at https://tinyurl.com/y4lchxk7. A California regulation and quarantine boundary map can be found at http://tinyurl.com/y3ftxzzu.
How you can help. Monitoring citrus for the presence of the ACP and symptoms of HLB is key for controlling this fatal disease. Inspect your citrus any time there is a flush of newly developing leaves; especially in springtime (now), and later on the fall flush. Like aphids, psyllids feed on new, developing leaves. Look for evidence of the ACP in new growth by checking for:
- Adult psyllids feeding, head down and rear end in the air (a 45 degree angle)
- Twisted or notched leaves in new growth
- Sticky honeydew and black sooty mold
- Nymphs that produce waxy, white tubules
- Tiny, yellow, almond-shaped eggs
Control ants that like to “farm” the psyllid honeydew to feed their young. Ants will protect the psyllids from their natural enemies such as parasites and other predators. Only purchase citrus trees from reputable sources and DO NOT transport citrus trees, fruit, or cuttings from areas known to harbor the psyllid.
If you suspect the presence of the ACP or any evidence of HLB disease, immediately contact the Butte County Agricultural Commissioner's Office (530-538-7381), or the CDFA Citrus Threat hotline (800-491-1899).
Sources for more information include:
The UC IPM Publication for ACP and HLB Disease at http://tinyurl.com/yy6jtgy9
California Department of Food and Agriculture at https://www.cdfa.ca.gov/plant/acp/
Citrus Pest & Disease Prevention Program at http://californiacitrusthreat.org/
For more information on gardening in our area, visit the Butte County Master Gardener web page at: http://ucanr.edu/sites/bcmg/. If you have a gardening question or problem, call our Hotline at (530) 538-7201 or email mgbutte@ucanr.edu.
All photos are from the University of California Division of Agriculture and Natural Resources (ANR).
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
UC does not have any recommendations for the home gardener to deal with this. It will likely not damage the tree, but the lemons can look pretty bad and will not keep well. The infection does not penetrate beyond the rind. As you've seen, the inside of the lemon is still good.
The best advice is to remove all the fruit once the weather has dried and to remove and dispose (i.e., green can) of any fallen leaves and fruit from around the tree. This is to remove as much of the fungal material as you can. The spores were probably on the ground and were splashed up into the tree when it rained. Add fresh mulch in that area which will help to cover up existing spores. Do this after the weather becomes dry (be sure to leave the trunk area clear of mulch by 4”). You can also thin out some of the canopy to let in more light and air, but don't prune while it is wet. Dispose of the tree pruning into the green can too. With the recommended effort hopefully, you can stop this pest and have lemons next year.
Please don't hesitate to contact us again if you have more questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
| Don't miss our 2019 Great Tomato Plant Sale - Walnut Creek 3/30, Richmond 4/6, Antioch 4/13. Click here for more information:http://ccmg.ucanr.edu/tomato/ |
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog.
- Author: Cris L. Johnson
The "Citrus Production Manual" covers the step-by-step process for preparing citrus for production and includes information on diseases and other issues that can affect citrus.
According to the ANR catalog website the manual will assist growers "From deciding scion variety and rootstock, to establishing an orchard, to managing production, to postharvest handling, you'll find it all here in a readable format. Colorful photos and clear diagrams and illustrations guide you through important concepts."
The manual costs $75 and you can order this publication click on the following link.
http://anrcatalog.ucdavis.edu/Details.aspx?itemNo=3539
Or you can save 25% by bundling the "Citrus Production Manual" with the 3rd edition of "IPM for Citrus" for a cost of only $10 more ($85 for both!). Order the bundle by clicking on the following link.
http://anrcatalog.ucdavis.edu/Details.aspx?itemNo=3539PROMO
SAVE 10% when you order this manual using the promo code "PREVEN56." This code extends the discount to you and provides a portion of the sale to UC Cooperative Extension Ventura which goes toward maintaining our local programs here.
