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Topics in Subtropics Blog!

Five Snail Speakers for the Price of One

Snails and Slugs (May 22, 2019 from 3-4pm)

Presenters: (!) Dr. Cheryl Wilen (UC IPM), (2) Dr. Rory Mc Donnell and (3) Dr. Dee Denver (Oregon State University), (4) Dr. Adler Dillman and (5) Dr. Irma De Ley (UC Riverside). The webinar will cover an overview of snail and slug biology, damage and management with emphasis on brown snail and Italian white snail, and current research on slug biocontrol using nematodes. One DPR CE unit (other) and one CCA CE unit (IPM) are approved.


And What Else Are the

                   UC Ag Experts

                             Talking About? 

Event NameDate
UC Ag Experts Talk: Snails and slugs 5/22/2019
Uc Ag Experts Talk: Management of Weeds in Citrus Orchards 6/19/2019
UC Ag Experts Talk: Citrus Dry Root Rot 7/24/2019

What is involved in the webinars?

A series of 1 hour webinars, designed for growers and Pest Control Advisors, will highlight various pest management and horticultural topics for citrus and avocados.  During each session, a UC Expert on the subject will make a presentation and entertain write-in questions via chat during and/or after the presentation. As we develop this program, we may expand to other crops.  

Topics: pests and diseases of citrus, avocado and other crops

And Next up is:

Management of Weeds in Citrus Orchards (June 19, 2019 from 3-4pm)

Dr. Travis Bean, assistant weed science specialist in UCCE, will discuss the importance of weed management in citrus, tree age and variety considerations, scouting and weed identification, cultural and mechanical practices, and pre- and post-emergence herbicides. One DPR CE unit (other) and one CCA CE unit (IPM) are pending.

Register in advance for the webinars by clicking on the event links above.

Are there Continuing Education units?

When the subject discusses pest or disease management, continuing education units will be requested from DPR (1 unit per session).  Participants will pre-register, participate in the webinar and be awarded the unit.  The sessions will be recorded and hosted on this web site for future study.  However, continuing education units will be awarded only to the participants who attend the live version of the webinar.  

Who is involved?

This webinar series is brought to you by Ben Faber (UC ANR Ventura Advisor) and Dr. Beth Grafton-Cardwell (Depart of Entomology UC Riverside Extension Specialist) with the technical support of Petr Kosina (UC IPM Contect Development Supervisor) and Cheryl Reynolds (UC IPM Interactive Learning Developer).  

giant land snail
giant land snail

Posted on Wednesday, May 15, 2019 at 1:21 PM

Upcoming ACP-HLB Updates

Task Force to host Spring 2019 ACP-HLB update


Members of the Ventura County citrus community are invited to a workshop to review the most recent rounds of area-wide treatment, learn about plans for future treatment cycles, and hear about the latest research into psyllid suppression and disease management strategies.

The workshop will be from 9:30 to 11:30 a.m. on Thursday, May 23, at the Museum of Ventura County, 100 E. Main St., Ventura. The event is free, but advance registration is required. To reserve a spot, register online at


9:30 a.m.

Welcome, and update on status of HLB in California, including possible hot spots in Ventura County and quarantine implications for citrus operations:

Leslie Leavens, chair, Ventura County ACP-HLB Task Force.

10 a.m.

Scientific rationale behind voluntary grower action plan for HLB confirmations in commercial groves:

Neil McRoberts, western regional director, National Plant Diagnostic Network, and associate professor of plant pathology, UC Davis.

10:30 a.m. 

Managing Asian citrus psyllid and HLB in Southern California commercial groves:

Beth Grafton-Cardwell, IPM Specialist and Research Entomologist, University of California-Riverside, and Director of Lindcove Research and Extension Center.

11 a.m. 

Area-wide treatment completion rates for 2018-2019, and treatment schedule for 2019-2020:

John Krist, CEO, Farm Bureau of Ventura County.

11:15 a.m.

Audience Q&A

11:30 a.m.


Click here to download a copy of the treatment schedule for 2019-2020.

New Huanglongbing Detection in Riverside


A residential citrus tree in the city of Riverside has tested positive for Huanglongbing (HLB). The citrus tree was located on a previous detection site from 2017. This is the first HLB detection in Riverside County since 2017. The California Department of Food and Agriculture is in the process of removing the HLB-positive tree.

In addition to removing the HLB-positive tree, CDFA has pulled samples from all other citrus trees on the property for testing and is in the process of beginning treatment of all host plants within 400 meters of the detection site.

Since this new detection occurred on the same property as a previous find, there will not be a change to the current HLB quarantine area or Asian citrus psyllid quarantine zones.

Citrus growers and pest control advisers in Riverside County should reach out to the county's Grower Liaison Alan Washburn at or 951-683-2392 with questions and to seek recommendations on how to protect their orchards.

HLB symptoms
HLB symptoms

Posted on Wednesday, May 15, 2019 at 6:18 AM

Hot off the Subtropical Internet

The latest newsletter from the UCCE Subtropical Crops Advisors and Specialists is available to read now:

TOPICS IN THIS ISSUE – Craig Kallsen, Editor


  • Introducing Your New Information Source for CDFA grants, Kern and Ventura Counties


  • Spotlight on SWEEP in Citrus


  • Low Pressure Guide to Low-Flow Irrigation Scheduling


  • The So-Called “Leaf Fleck” Virus Diseases of Citrus


  • Replanting Trees in Mature Citrus Groves


  • What about Planting Lemons in Kern County?

Posted on Monday, May 13, 2019 at 5:19 AM

Citrus IPM Update

It's not easy to update the IPM Handbook in paperback, but You can check out the latest IPM Pest Management Guidelines for arthropod pests at:

The other sections will be updated soon.  Tune in, and in the meantime if you don't have a copy of the IPM Manual, it's time to get one:

How to order

Obtain Integrated Pest Management for Citrus from the UC ANR catalog, or by mail, by telephone, and at many of the UC County Cooperative Extension offices. For more information, see "How to Order Publications."


Third Edition
Integrated Pest Management for Citrus

Published 2012 · Publication 3303 · 275 pages

How to order
List of contents
  Book excerpts:
General predators in citrus (2.9 MB, PDF)
Fruit disorders in citrus (PDF)

Cover of Integrated Pest Management fpr Citrus.

Integrated Pest Management for Citrus is the best-illustrated guide available for the prevention, identification, monitoring, and management of citrus pests. This book also provides substantial information on citrus production practices that prevent pest problems. More highly illustrated and extensively revised during its third edition, this book presents pest information and management recommendations from University of California Cooperative Extension specialists, farm advisors, and researchers.


Third edition revisions include:

  • more than 300 additional photographs
  • more illustrated keys to help you distinguish among similar-looking pest species
  • new pests and foreign species to look-out for
  • updated monitoring and pest management recommendations
  • effective use of natural enemies, cultural controls, and other pest-prevention methods

High-quality Photographs

More than 500 high-quality color photographs and dozens of drawings and charts will help you identify and manage over 150 different citrus pests and to recognize the important natural enemies of pest insects and mites. The book content includes pest insects, mites, diseases, weeds, nematodes, and vertebrates. Abiotic disorders and crop production and harvest-related problems are also covered.

citrus manual
citrus manual

Posted on Friday, May 10, 2019 at 5:44 AM

New News About HLB

By John Krist

Chief Executive Officer of the Farm Bureau of Ventura County. Contact him at

Nearly 600 scientists, government agency representatives and members of the agricultural community gathered in Riverside last month for the sixth International Research Conference on HLB. This was the first iteration of the IRCHLB to take place in California, but like its predecessors in Florida, the conference drew a global sampling of smart people trying to figure out an answer to the most pressing question facing the worldwide citrus industry: How do we stop Huanglongbing and the Asian citrus psyllid from destroying it?

As was the case at previous conferences, no definitive answer to that question was provided by any of the hundreds of research presentations and posters. Work continues on every imaginable mechanism for disrupting the lethal vector-host-pathogen complex: breeding HLB-resistant or HLB–tolerant citrus rootstocks and scions; disrupting the ability of ACP to reproduce, feed or acquire the disease-causing bacteria; treatments to cure or reduce symptoms of infection; genetically or biologically based methods for killing ACP more efficiently. The “solution,” however, remains as elusive as it was during all previous biennial conferences.

But there have been important advances. This year, researchers presented results from their use of a tool that did not exist as recently as seven years ago. And it offers the prospect of rapid development of a suite of interventions — HLB-tolerant trees, crippled psyllids, perhaps even a lethal agent that attacks the bacteria themselves — that could change the course of the epidemic.

The new approach is being made possible by a gene-editing technology known as CRISPR. The term (pronounced “crisper”) is an acronym for “Clustered Regularly Interspaced Palindromic Repeats,” and it refers to odd DNA fragments discovered 20 years ago by scientists examining the genome of various families of microbes.

The short, repeated fragments of DNA were distinctive and appeared unrelated to the remainder of the microbial genome. Additional investigation revealed similar structures in the genomes of microbes from vastly different families of life, suggesting that they were not random but performed some function useful to microbial survival.

Research over the next decade revealed that CRISPRs were a feature of bacterial immune systems. Bacteria attacked by viruses (known as bacteriophages, or just phages) evolved a way to duplicate small snippets of the invader's DNA, insert it into their own genome, and pass that modified genetic code along to subsequent generations of bacteria. If attacked again by a phage containing that same snippet of DNA, the bacterial DNA recognizes it and triggers a targeted enzyme response that severs the viral genome at precisely that point, disabling the virus.

These discoveries led eventually to a technique by which researchers can pretty much treat the genome of any organism as a set of Lego blocks, its pieces plugged in, removed or replaced virtually at will. Using tools developed in the lab, but replicating the function of the CRISPR complex in microbes, they can dispatch custom-made genetic packets into living organisms, where they can remove, silence, activate or replace specific genes and their functions. 

Since scientists first reported six years ago that this adaptive microbial immune system could be repurposed into a simple and reliable technique for gene editing, thousands of researchers have been exploring its application in a wide variety of fields. One of them is the quest for a solution to HLB. And at this year's conference, several teams reported progress toward using the CRSPR system to modify the genome of all three elements of the pest-host-disease triad: ACP, the HLB bacteria, and citrus trees. 

Perhaps the most remarkable of these reports carried an inscrutable title: “BAPC-assisted-CRISPR-Cas9 Delivery into Nymphs and Adults for Heritable Gene Editing (Hemiptera).” 

Hidden within that bland language was a dramatic achievement: Two scientists — Wayne Hunter at the U.S. Department of Agriculture's Fort Pierce lab in Florida, and John Tomich of Kansas State University — injected a special variant of the CRISPR package, designed to knock out two genes in the ACP genome, into a female adult psyllid. Her offspring inherited a CRISPR-modified genome in which those two genes — one governing physiological development, and the other eye color — had been deleted. 

As nymphs, the genetically modified ACP took much longer to develop and had lower survival rates. As adults, the survivors had strange white eyes and malformed wings, and their lifespan was one-third of normal.

Those would be useful achievements on their own. But the experiment also demonstrated a powerful tool for determining the functions of other ACP genes by disabling them and observing the results on psyllid morphology, physiology or behavior. This could potentially lead to one of the Holy Grails of ACP-HLB research — a psyllid that is incapable of transmitting the disease-causing bacterium. 

Driving that genetic trait throughout the ACP population would halt the epidemic in its tracks. Growers could greatly reduce, if not eliminate, their reliance on pesticides as a means of slowing disease spread by suppressing the vector population — currently the only viable strategy. 

There were several other presentations about research to use CRISPR or other techniques to genetically modify the citrus genome to improve HLB tolerance — a much more rapid way of generating potential new rootstocks than the years-long process required to screen varieties and rear new trees — and to disable or kill the bacteria themselves.

The speed with which this field of knowledge is evolving, and the remarkable power of the CRISPR technology, left many of us who heard these presentations hopeful. After years of tantalizing research “breakthroughs” that have failed to yield meaningful and deployable interventions, the fight against ACP and HLB may soon be waged on our terms – not the bug's. 

Until transgenic psyllids move from the lab to the field, however, we're stuck with our current approach to disease and vector management: Suppress ACP populations with chemicals, identify and remove infected trees as quickly as possible, and replant using disease-free nursery stock. But there was exciting news on this front as well. 

From the beginning, the effort to identify and remove HLB-positive trees has been hampered by the long lag time between initial infection and confirmation using the classic DNA testing that serves as the regulatory gold standard. Because the test looks specifically for sequences of DNA that are unique to the bacteria in samples of ACP or plant tissue, it can provide incontrovertible and direct evidence of infection. From a legal standpoint, this is key when regulators act to force removal of positive trees. 

The problem, however, is one of sampling. A mature citrus tree may have 200,000 leaves, yet in the early months and even years of infection, the bacteria are not distributed uniformly through the canopy. Typical samples submitted for DNA analysis may consist of as few as 12 leaves per tree. Chances of picking the right leaves are minuscule when the bacterial population is small, and perhaps isolated only in a particular branch. The odds are stacked against the sampling effort from the start. 

This is why a major branch of the global research effort is devoted to developing early detection technologies — methods of confirming probable HLB infection based on changes in tree physiology that come about within days or weeks of infection. Being able to identify and remove infected trees before significant numbers of ACP have had the opportunity to feed on them and acquire the bacteria would greatly improve our ability to influence the course of the epidemic.

Several good candidates have been identified and validated, but they require intensive laboratory processing, and capacity limitations have stymied their wide use. But the most promising of these technologies doesn't require a lab at all.

As reported here after the 2017 IRCHLB, a team of dogs trained according to protocols developed by researchers at USDA and North Carolina State University have demonstrated the ability to correctly identify HLB-positive trees as little as two weeks after infection. During field trials, their accuracy rate has been up to 98 percent.

From the outset of this project, which has been funded through a federal grant, lead researcher Tim Gottwald of the USDA theorized that the dogs were identifying a change in the suite of volatile organic compounds emitted by trees. This is known to occur almost immediately upon infection, as the plant mounts a physiological defense against the invading bacteria. Sick trees don't smell like healthy trees, and Gottwald's theory has been that dogs can tell the difference.

At this year's conference Gottwald declared that he'd been wrong. In more recent experiments, his team injected the HLB bacterium into plants that are utterly unlike citrus — periwinkle, tobacco, dodder. Although the dogs had been trained on citrus, they correctly identified the inoculated non-citrus plants even though they smelled nothing like oranges or lemons. He then took it one step further, and ran the dogs past cages containing ACP, some of which had been infected in the lab. The dogs were able to correctly identify infected psyllids as well. And bugs don't smell anything like plants.

To confirm his new hypothesis, he exposed the dogs to an array of bacterial cultures, some of which included the bacteria known to cause HLB. The dogs were able to identify those, too. Gottwald now believes that when the dogs identify citrus tree as infected with HLB, it's because they are picking up the actual scent of the bacteria within it. 

If that's the case, it would provide a powerful argument for immediate and mandatory removal of suspect trees very early in the disease process: The dogs would providing direct evidence of infection. From a regulatory standpoint, it should be no different from a positive DNA test result.

The current risk-based HLB survey being conducted throughout the state — consisting of systematic collection of plant tissue and psyllid samples for DNA testing — has been heavily weighted toward urban areas, which is how the exploding epidemic in Los Angeles, Orange and Riverside counties was discovered. The current tally of HLB-positive trees removed there now exceeds 1,200, all of them in urban yards. 

Less attention has been paid, however, to rigorous surveying of commercial groves. This places an imperative on arranging for trained dogs and handlers, now based in Florida,  to begin their work here. Nothing is more important than finding HLB in commercial groves while it is early enough for tree removal to stop or slow the spread of the epidemic. The CRISPR research has opened the door to an entirely new array of potential weapons against HLB, but the citrus industry needs to survive long enough to use them.


HLB deformed fruit

hlb defprmed citrus
hlb defprmed citrus

Posted on Wednesday, May 8, 2019 at 6:26 AM

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