Posts Tagged: asian citrus psyllid

ACP Updates

 Asian Citrus Psyllid Update

Winter and spring rains have given us a robust growing season this year. Tender new citrus flush is ideal habitat for ACP to feed, lay eggs and build new populations. An increase in ACP numbers and feeding can increase the risk of HLB spreading and building up. University of California recommends growers monitor trees regularly for ACP, paying careful attention to new flush, and treat when populations reach the detection threshold.  The UC IPM website lists a range of materials effective against ACP, including organic options. Growers are also encouraged to work with a pest management professional to better detect and manage ACP.

Advanced notification of nearby beekeepers is required before pesticide treatments. Use the BeeWhere BeeCheck system, or contact the County Agricultural Commissioner's office, 805-681-5600, for more information. Always follow label instructions for bee safety. 

If your citrus is no longer being cared for or is not worth the resources required to protect it from ACP and HLB, consider removing it.

HLB Quarantine Update

As of May 5, a total of 5.007 trees and 709 ACP have been confirmed positive for the bacterium that causes HLB. Trees confirmed positive are treated for ACP and removed, and the HLB quarantine may be expanded. Additional ACP treatments and HLB detection surveys are conducted on a recurring basis to remaining citrus within 250 meters of each detection.

Counties where HLB has been detected via PCR testing are Los Angeles, Orange, San Diego, Riverside, San Bernardino and San Diego, with the majority of detections in Orange County. To see a map of the current HLB quarantine areas, and other details of locations and numbers of HLB detections, please visit maps.cdfa.ca.gov/WeeklyACPMaps/HLBWeb/HLB_Treatments.pdf. 

HLB Detection Response Guide for Growers 

To ensure California citrus growers are well prepared in the event of a potential commercial grove detection of Huanglongbing (HLB), the Citrus Pest and Disease Prevention Program (CPDPP) has developed the  Response Guide for a Confirmed HLB Positive Detection in a Commercial Grove, which details the steps taken by CDFA and actions required of the property or grove owner, as outlined in CDFA's Action Plan and Information for Citrus Growers/Grove Managers.

Citrus Pest and Disease Prevention Committee Meetings -- Webinar and In Person 

All meeting agendas and eventually the minutes are posted at www.cdfa.ca.gov/citrus committee/. The 2022-23 schedule for the Full Committee is here, and the schedule for Subcommittees is here.

Upcoming Meetings

• Operations Subcommittee, Wednesday May 10 at 9 am (agenda and webinar link)
• Outreach Subcommittee, Wednesday May 10 at 1:30 pm (agenda and webinar link)
• CPDPP Full Committee, Wednesday August 9 (agenda pending)

All meetings are free and open to the public to listen to or make public comment. Meetings are currently in person and accessible via phone and/or webinar. Links to register for and join meetings are included in agendas when posted.

For a list of current committee members, click here. 

Additional ACP/HLB Resources

• CDFA Citrus Division website: https://www.cdfa.ca.gov/Citrus/
• General ACP/HLB

oInformation on the state ACP/HLB program including maps, quarantine information, and a signup option for email alerts: citrusinsider.org/

oBiology of ACP and HLB, detection maps and recommendations for monitoring, eradication and management: ucanr.edu/sites/acp/ 

oUC IPM recommendations for ACP insecticides

oWeb-based map to find out how close you are to HLB: ucanr.edu/hlbgrowerapp

oVideo on Best Practices in the Field, available in English and Spanish

oSpanish-only ACP/HLB presentation video presentation and audio-only recording. 

• Research

oLatest Science Advisory Panel Report

oUC Ag Experts Talk presentations on management of various citrus pests and diseases are available for viewing here and here on YouTube.

oSummaries of the latest research to combat HLB: ucanr.edu/sites/scienceforcitrushealth/

oScience-based analyses to guide policy decisions, logistics, and operations: www.datoc.us

• Regulatory/Quarantine

oSign up for program updates from the Citrus Pest and Disease Prevention Division at www.cdfa/signup-email-updates.

oRegulatory requirements for moving bulk citrus: Information for Citrus Growers

oSummary of regulatory requirements in the event of an HLB detection in commercial citrus: citrusinsider.org/Regulatory-Flyer

oSanta Barbara County Ag Commissioner's Office

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Cressida Silvers

CA Citrus Pest and Disease Prevention Program

ACP/HLB Grower Liaison

Ventura, Santa Barbara and San Luis Obispo Counties

805 284-3310 (phone or text)

acp (2)

ACP and Biological Control

ACP and nypmphs

ACP and Natural Enemies

Natural enemies have significantly suppressed Asian citrus psyllid populations in southern California

Ivan Milosavljevi, Department of Entomology, University of California, Riverside, CA

Christina D. Hoddle, Department of Entomology, University of California, Riverside, CA

David J.W. Morgan, California Department of Food and Agriculture, Mt. Rubidoux Station, Riverside CA

Nicola A. Irvin, Department of Entomology, University of California, Riverside, CA

Mark S. Hoddle, Department of Entomology, University of California, Riverside, CA

Is California facing a citrus apocalypse?

Asian citrus psyllid (ACP) (Diaphorina citri)  is an invasive pest of citrus first discovered in urban citrus in San Diego County California (CA) in 2008 . ACP presents a significant economic threat to CA's citrus industry because it vectors a bacterium, CLas, which causes a citrus-killing disease, huanglongbing (HLB). There is currently no cure for HLB which kills susceptible commercial citrus varieties in as little as 5 to 8 years. Since HLB was first discovered in Florida (FL) in 2005 (ACP was discovered in FL in 1998), citrus production in that state has fallen by 80% . In CA, the first case of HLB was detected in 2012 in Los Angeles County and infestations of ACP-CLas are largely restricted to urban-grown citrus in southern CA. Should HLB spread north into the San Joaquin Valley, where 75% of CA's citrus fruit is grown, it would jeopardize ~262,000 fruit-bearing acres, which generates over $3 billion annually and provides over 26,000 jobs. Because ACP-HLB poses such a significant threat to CA's citrus industry, ACP population suppression is key to slowing the spread of CLas into CA's commercial citrus groves.

Biocontrol suppresses ACP populations

In CA, ACP has been the target of a classical or introduction biological control program with two tiny parasitic wasps or parasitoids, Tamarixia radiata and Diaphorencyrtus aligarhensis, sourced from Pakistan, a part of the ACP's presumptive native range. CA's biocontrol program against ACP began with the release of T. radiata in December 2011, and in December 2014, D. aligarhensis was added to the release program with the intent of establishing a complementary set of parasitoids that specifically attack ACP nymphs. To date, >24 million parasitoids (T. radiata and D. aligarhensis combined) have been mass-produced and released at >19,500 sites in southern CA by the Applied Biocontrol Lab at UC Riverside and the California Department of Food and Agriculture. Of these two parasitoids, T. radiata established readily and rapidly spread into sites in CA where it was not released. Conversely, D. aligarhensis failed to establish following release in CA and mass production and release of this parasitoid was subsequently discontinued in 2019.

The ongoing biocontrol effort: So far, so good, but there is room for improvement

Since the inception of the ACP biocontrol program in CA in 2010 and the first release of T. radiata in 2011, densities of ACP infesting urban citrus have declined by ~70%. Two different multi-year and multi-site studies in urban citrus in southern California has clearly demonstrated that the proximate causes of these widespread population declines are due to natural enemies, specifically parasitism of ACP nymphs by T. radiata and predation by generalist predators, of which syrphid fly larvae are key predators of ACP nymphs . Consequently, reduced ACP densities may have slowed the spread of CLas in CA and subsequent development of HLB in infected citrus trees. However, the efficacy of natural enemies attacking ACP eggs and nymphs has been reduced by the presence of another invasive pest, the Argentine ant (AA) (Linepithema humile). Field work on ACP biocontrol in CA identified AA as a significant impediment to natural enemies. When present on trees, AA reduced the abundance of natural enemies interacting with ACP and suppressed the efficacy of T. radiata and syrphids by over 50 percent. When AA is excluded from ACP colonies, natural enemy abundance and attack rates increase significantly, particularly impacts by T. radiata and syrphid fly larvae.

Why are Argentine ants problematic, and what can we do about them?

AA aggressively protect >55% of ACP from natural enemies. In return for this protection, AA is rewarded with food, honeydew, which is a sugary waste product excreted by ACP nymphs. Consequently, AA protection exacerbates infestations of ACP and other honeydew producing pests in citrus (e.g., brown soft scale and mealybugs). This results in a positive feedback loop – more pests survive due to AA protection and their populations increase which in turn produces more food for AA which results in increasing ant populations. An undesirable outcome of these population increases is greater applications of insecticides to control sap sucking pests and AA. Ironically, sprays of contact insecticides targeting AA (and ACP) kill natural enemies needed for “free” pest control and this disrupts IPM programs which aim to reduce insecticide use.

To ameliorate this problem of increased insecticide use, biocontrol ACP (and other sap sucking pests) can be enhanced through three management practices: (1) monitoring AA activity with infra-red sensors to determine when ants have reached densities that need controlling, (2) controlling AA with highly targeted applications of ultra-low concentrations (i.e., 0.0001%) of insecticide delivered to foraging inside of biodegradable hydrogel beads that are infused with 25% sucrose water and insecticide, and (3) floral resources that provide food and shelter to natural enemies, especially hover flies, that attack ACP nymphs. This three-pronged management approach for controlling AA and the pests ants protect (e.g., ACP) is undergoing field evaluation in commercial citrus orchards in southern California. The outcomes of these large, replicated field trials will be discussed in an upcoming article in Topics in Subtropics: “Maximizing IPM of Argentine ant and sap sucking pests with biodegradable hydrogels, infra-red sensors, and cover crops in commercial citrus orchards.”

aRGENTINE ANT

HLB Update

As of December 4, a total of 2,196 residential trees and 321 ACP have tested positive via PCR for the bacterium that causes HLB. See the latest HLB map and table for details: maps.cdfa.ca.gov/WeeklyACPMaps/HLBWeb/HLB_Treatments.pdf.  As before, the infected trees have been or are being removed, and ACP treatments are applied on a recurring basis to remaining citrus in those areas. To date, no HLB has been found in commercial trees via PCR testing. The HLB quarantine area, however, includes commercial citrus and continues to expand.

Please refer to the CDFA Action Plan for ACP and HLB for information on regulatory and treatment requirements to expect should HLB be detected in or near your citrus grove or packing house. 

Best Practices in the Field

In addition to monitoring and treating for ACP, another important way to protect your citrus from ACP and HLB is to follow Best Practices in the field, including insisting that all equipment, vehicles and bins be free of all plant material before entering your property.

Download or stream this video to help refresh field crews on the best practices for avoiding the spread of ACP and HLB during harvest.

ACP/HLB Resources

• Sign up for program updates from the Citrus Pest and Disease Prevention Division at www.cdfa/signup-email-updates.
• General information on the state ACP/HLB program including maps, quarantine information, and a signup option for email alerts: citrusinsider.org/
• Biology of ACP and HLB, detection maps and recommendations for monitoring, eradication and management: ucanr.edu/sites/acp/ 
• UC Ag Experts Talk presentation "ACP for Commercial Growers and Pest Control Advisors", now available for viewing, along with other past talks on various citrus pests, at https://ucanr.edu/sites/ucexpertstalk/Past_Webinars/
• Web-based map to find out how close you are to HLB: ucanr.edu/hlbgrowerapp
• Summaries of the latest research to combat HLB: ucanr.edu/sites/scienceforcitrushealth/
• Science-based analyses to guide policy decisions, logistics, and operations: www.datoc.us

ACP Update

ACP trap detections have increased recently on the coast and in the Central Valley. While we usually see trap numbers peak this time of year, this fall the numbers have been higher than the last few years. Please stay vigilant in monitoring your trees for ACP, treating for ACP during the Area Wide Management treatment windows, and using an ACP-effective insecticide if possible when conducting other orchard management applications. 

Map of HLB Quarantine and Treatment Area in California

HLB quarantine area 2020 dec

First study to compare citrus varieties with combination of metabolomics and microbiome

Citrus greening disease, or Huanglongbing (HLB), is deadly, incurable, and the most significant threat to the citrus industry. Most HLB research focuses on the tree canopy, but scientists in California studied the impact of HLB on root systems. They recently published the first study to report on the response of two different varieties of citrus to the causal bacterium, 'Candidatus Liberibacter asiaticus' using metabolomics and microbiome technologies.

"Metabolomics is a cutting-edge field of study that provides snapshot information about the metabolism of living things," explains author Emily M. T. Padhi, "while microbiome studies provide valuable information about the microbial communities living in a particular ecological niche - some microbes are beneficial to the host, while others can be harmful."

Padhi and colleagues wanted to see how the root system of two varieties of citrus responded to HLB. They collected roots from healthy and infected Lisbon lemon and Washington Navel orange trees grown in greenhouses at the same time and under the same conditions.

They found that both varieties experienced a reduction in root sugars and amino acids when exposed to HLB. However, they also found differences. While the concentration of malic acid and quinic acid (two metabolites involved in plant defense) increased in the navel roots, they decreased in the lemon roots. They also found that the beneficial bacteria Burkholderia increased substantially in navel plants but not in lemons, which contradicts previous studies.

"Overall, this is the first study to compare two varieties of citrus using a combined metabolomics and microbiome approach and demonstrates that scion influences root microbial community composition and, to a lesser extent, the root metabolome."

There is evidence to suggest that the causal bacterium moves to the root system soon after a plant becomes infected. A key strategy for preserving the health of an infected tree is root system management and research on different responses to HLB may help devise new variety-specific preventative and treatment measures.

Emily M. T. Padhi Nilesh Maharaj Shin-Yi Lin Darya O. Mishchuk Elizabeth Chin Kris Godfrey Elizabeth Foster Marylou Polek Johan H. J. Leveau and Carolyn M. Slupsky

https://apsjournals.apsnet.org/doi/10.1094/PHYTO-03-19-0103-R

Images of the bulk root mass and sample leaves from healthy and 'Candidatus Liberibacter asiaticus' lemon and navel plants.

Credit: Emily M. T. Padhi, Nilesh Maharaj, Shin-Yi Lin, Darya O. Mishchuk, Elizabeth Chin, Kris Godfrey, Elizabeth Foster, Marylou Polek, Johan H. J. Leveau, and Carolyn M. Slupsky

HLB infected roots

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