- Author: Sonia Rios
The University of California Cooperative Extension is hosting free workshops for citrus grove owners, managers and farmers. The workshop will provide an overview of proper Asian citrus psyllid (ACP) scouting techniques from University of California research entomologists Dr. Monique Rivera. Attendees will have the opportunity to practice psyllid scouting techniques in blocks of trees known to host ACP.
- No cost to attend this event
- Strongly encouraged to bring a hand lens (a loaner hand lens will be provided if needed).
- 1.5 of “other” DPR Continuing Education Hours will be given.
- Further details on workshop location will be provided to registrants by email 48 hours prior to the event.
Space is limited, please register at: http://ucanr.edu/survey/survey.cfm?surveynumber=25658
October 2, 2018, 9-11 AM
If you have any questions, please contact:
951-683-6491 EXT 224
- Author: Ben Faber
- Author: Sara Garcia Figuera, Jennifer Reed and Brianna McGuire
Western Plant Protection Network at UC Davis
Early detection technologies (EDTs) are tests that indicate the presence of disease before signs or symptoms of the disease can be seen. In the same way that a doc-tor measures a patient's blood pressure to look for heart problems, a grower might use a trained “sniffer” dog to detect changes in a tree that looks healthy but has huanglongbing (HLB) disease. By using the EDT, the grower is able to uncover HLB earlier, and can decide on an early, cost-saving course of action.
In the case of HLB, there are many EDTs under development. Some of them look for patterns in the microorganisms that live on the citrus leaves (Leveau snapshot); some look for patterns in the chemicals that are produced by the tree in response to HLB (Pourreza, Davis and Slupsky); and others look for the molecules that the bacterium injects in the tree to cause disease (Ma). A description of some of these EDTs can be found on the Science for Citrus Health website.
Why do we need EDTs for HLB?
To understand why EDTs are needed and what their potential value is, it is necessary to understand the difference between the incubation period for a disease and the latent period. The incubation period is the time between exposure to the pathogen and the appearance of symptoms. The latent period is the time between exposure and the newly-infected host becoming infectious. Huanglongbing (HLB) has a long incubation period and a very short latent period, which means that a tree can be dis-eased for a long time without showing any visible symptoms, while being infectious for a large fraction of that time. Even if a tree does not seem diseased, it can serve as a home for the bacterium (Candidatus Liberibacter asiaticus, CLas) that causes HLB. If a psyllid feeds on the infected tissue of a tree (with or without symptoms), CLas that is present in the leaf tissue can be picked up by the insect and transmitted to other trees when the psyllid moves on to feed. Information from an EDT can help a grower detect the disease in a tree a long time before it would be detected by eye. This cuts down the time psyllids are able to feed on it and transmit the disease, slowing the spread of HLB to neighboring trees.
Why is it important to remove infected trees as early as possible?
If a tree that tests positive for CLas is not treated or removed, the bacterium will spread throughout the tree. Over time, an increasing proportion of the tree's tissues will become infected, increasing the chances that a psyllid will become infected upon feeding, and subsequently spread the infection to healthy neighboring trees. If the infected tree is removed, there is no opportunity for psyllids to feed on the infected tissue and spread the disease. Once CLas is detected, tree removal is the only surefire way to prevent the spread of the infection, and it is extremely time-sensitive. The sooner an infected tree is removed, the lower the chances that psyllids will get infected. The savings associated with early infected tree removal will be proportional to the amount of surrounding trees that would have been infected with CLas due to that tree, and the number of months that it would be left on the ground.
Who is working on the project?
Several research teams in different universities and research stations, supported by a variety of funding organizations, have been working on the development of a variety of EDTs. These EDTs, designed under laboratory and greenhouse conditions, are being validated under field conditions in Texas and Florida. In California, where HLB has not been detected in citrus orchards, samples of different citrus varieties have been collected from healthy trees and trees affected by other diseases from all over the state. These samples are being used to calibrate the EDTs, and to test if they can distinguish between healthy and HLB-diseased trees, and between HLB-diseased trees and trees affected by other common citrus diseases. Dr. Neil McRoberts and his team at UC Davis are evaluating the data from these experiments and providing support to the EDT researchers.
What are the challenges and opportunities?
Currently, regulations require HLB infected trees to be removed if a certain amount of CLas DNA is detected in leaf samples through polymerase chain reaction (PCR). However, CLas is unevenly distributed in the sap of citrus trees, and the leaf samples collected might not be PCR-positive even though the bacterium is already present elsewhere in the tree. EDTs offer the possibility to detect infected trees before they are PCR-positive, so they could be removed earlier in the HLB epidemic. Therefore, the value of EDTs relies on the voluntary removal of EDT-positive trees before the law requires them to be removed.
No EDT gives perfect diagnostic results. Sometimes healthy trees will produce EDT scores that look like diseased trees (so-called “false positives”). Removing such trees will result in an immediate financial loss. However, because the economic damage caused by leaving an infected tree in place is much bigger than the value of a healthy tree, using an EDT to guide decisions has the potential to result in a long-term economic benefit to individual growers and communities, by reducing the spread of HLB. Losing a few healthy trees along the way is the unavoidable cost of stopping the disease from spreading. Like-wise, some trees will seem healthy based on EDT scores but might end up showing symptoms (“false negatives”). The proportion of true positives, false positives, true negatives and false negatives represents the accuracy of a diagnostic test. Dr. McRoberts' team is analyzing the accuracy of the EDTs, and preliminary results suggest that the best performing EDTs could be correctly determining the status of the trees 95% of the time.
The results of this analysis could be used to foster the adoption of EDTs among the citrus grower community, promoting the idea that the sooner infected trees are detected and removed, the smaller impact HLB will have on California's citrus production. Unless there is sufficient cooperation in integrated management of HLB by removing infected trees as early as possible, controlling the ACP on an area-wide scale, and using certified plant material, the California citrus industry is likely to suffer un-sustainable economic losses to HLB.
- Author: Ben Faber
UC to conduct ACP scouting workshops
Registration is now open for Asian citrus psyllid scouting workshops to be conducted in Fillmore and Moorpark on July 13. Intended for grove owners, managers or farm employees, the sessions will provide instruction in ACP population monitoring as a way of improving the area-wide management (AWM) strategy in Ventura County.
At each workshop, University of California research entomologist Beth Grafton-Cardwell will provide an overview of proper scouting techniques, which participants will have the opportunity to practice in blocks of trees known to host ACP. Participants are asked to bring a hand lens (a loaner hand lens will be provided if you do not have one).
The workshops are free, but participation in each is limited to 25 people and advance online registration is required.
10 a.m. to noon in Fillmore. Register at https://acp-fillmore.eventbrite.com.
1:30 to 3:30 p.m. in Moorpark. Register at https://acp-moorpark.eventbrite.com.
Registered participants will receive details about the physical location of each workshop by email 48 hours before the event.
Science For Citrus Health
Interested in the research addressing Huanglongbing (HLB) disease? Check out the University of California website with the latest information. The site also has fact sheets, Powerpoint slides, and pictures that can be used for general outreach and presentation.
2018-2019 Area-wide treatments start soon for Ventura County
The next round of coordinated AWM treatments begin in mid-July, and reminders for the first ACP treatment window have been sent. If you did not receive a reminder, do not receive ACP email blasts, or need pest control/tree removal referrals, please contact your grower liaisons Sandra Zwaal and Cressida Silvers. Please remember to file Pesticide Use Reports (PURs) electronically and on a timely basis. Manually filed PURs can take months for recognition as an ACP treatment. For a no-cost CalAgPermits account to file electronically and for training, contact the Agricultural Commissioner's Office.
As of June 29, the total number of trees confirmed as infected by HLB had risen to 676. None were found in commercial groves. The HLB quarantine boundaries and the latest tally of HLB confirmations, updated weekly, is available online at https://citrusinsider.org/maps/. As confirmations increase and spread closer to commercial citrus, it is a good time to consider removing citrus trees not worth the resources required to protect them from ACP and HLB.
Meetings and resources
The Citrus Pest and Disease Prevention Committee will meet July 11 in Visalia. Attendance is free. Here is a link to the CDFA site with agenda, venue, and webinar information: https://www.cdfa.ca.gov/citruscommittee/
Feel free to contact your grower liaisons if you have questions.
- Author: Jeanette Warnert
The city of Riverside pitched a white tent over the "Parent Navel" orange tree at the intersection of Arlington and Magnolia avenues last week to protect it from the threat of huanglongbing disease, reported Ryan Hagen the Riverside Press Enterprise.
“The Parent Navel is an iconic symbol of Riverside, as it represents the impact the citrus industry had on our economy,” Mayor Rusty Bailey said in a press release issued by the City of Riverside. “Riversiders hold this symbol of our citrus heritage very dear, so it is encouraging to see our parks personnel taking a proactive approach.”
The tree was one of two planted by Eliza Tibbets in 1873, when she received the seedless orange cultivars from Florida by mail. Tibbets cared for the trees and sold budwood to nurseries, which led to extensive plantings of nursery trees cloned from hers.
Huanglongbing disease made its appearance in Riverside last year in residential trees. Officials are working to prevent its spread by controlling Asian citrus psyllid, the insect that can move the disease from tree to tree. Meanwhile researchers are searching for a cure.
The Parent Navel's high value led UC Riverside researchers and city officials to construct the large white barrier.
"It's not beautiful," said Georgios Vidalakis, UC Cooperative Extension specialist and director of the citrus clonal protection program at UC Riverside. "It's obstructing the tree from public view, and we apologize for that. But the risk from not doing that is catastrophic."