Voluntary Best Practices for Growers' Response to Huanglongbing
To provide California citrus growers with a strong toolbox of science-supported strategies and tactics to protect their orchards from Huanglongbing, the Citrus Pest & Disease Prevention Committee endorsed a set of best practices for growers to voluntarily employ in response to HLB in California.
The recommendations – which are grouped based on a grower's proximity to an HLB detection – represent the most effective tools known to the citrus industry at this time and are meant to supplement the California Department of Food and Agriculture's required regulatory response. They were developed by a task force consisting of growers from various regions across the state and scientists, including Dr. Beth Grafton-Cardwell and Dr. Neil McRoberts.
Growers are encouraged to use as many methods as feasible for their operation in order to limit the spread of the Asian citrus psyllid (ACP) and HLB, as the cost to manage the Asian citrus psyllid is far less than any potential costs or loss to the industry should HLB take hold throughout our state.
The Best Practices at a Glance
The complete best practices document, which includes the scientific rationale for the best practices, can be downloaded here. The following grid is intended to provide a brief, digestible format of the best practices.
At a recent workshop sponsored by the Ventura County ACP-HLB Task Force, presentations were made about the effectiveness of ACP suppression in the county, recommendations for voluntary grower responses to confirmed HLB-positive trees, area-wide treatment participation rates and other topics. The speaker presentations have been posted online, and are available for review at:
Canines can detect trees infected
with the bacterium
that causes huanglongbing
Research by Dr. Tim Gottwald
Article written by Tim Gottwald, Holly Deniston-Sheets and Beth Grafton-Cardwell.
Revised June 13, 2019.
What is the technique?
Canines have a highly sensitive scent detection capability that is significantly better (parts per trillion) than most laboratory instruments and they can be trained to “alert” (either sit or lay) when they detect specific ‘smells' (known as scent signatures). Most people are familiar with their ability to detect bombs, drugs, and plant material at airports. However, canines are also used to detect human pests, such as bed bugs, and agricultural pests, such as stink bugs, date palm weevils and imported fire ants.
With regard to agricultural pathogens, canines have been shown to detect with greater than 98% accuracy the fungal pathogen that causes laurel wilt disease in avocado, the bacterium that causes citrus canker disease in citrus, and plum pox virus in peach orchards.
Researchers have been training and evaluating the efficacy of canines for detecting “Candidatus Liberibacter asiaticus” (CLas), the bacterium that causes huanglongbing (HLB), for 5 years in Florida, and CLas detection efforts with canines have recently begun in California. Dogs have been trained in both the laboratory environment and in the field. Researchers have demonstrated that well-trained canines can detect CLas over 95% of the time in commercial trees and over 92% of the time in residential trees. Researchers did not observe any differences in canine performance between citrus species and varieties. The training that the canines receive is very specific to CLas. When they are taken into citrus orchards infected with citrus tristeza virus, viroids, the fungal pathogen Phytophthora, or the bacterium that causes citrus stubborn, the CLas-trained canines do not respond to these diseases.
Video of canine Maci running a row of trees in the Rio Grande Valley of Texas
The canines provide a significant opportunity to be used as an Early Detection Technology (EDT) in California. In a field study using potted citrus in Florida, dogs could detect CLas in some of the trees as early as 2 weeks after CLas-infected psyllids fed on the trees. In contrast, it can take 1-2 years for CLas to distribute itself in a mature citrus tree sufficiently for the bacterium to be present in sampled the leaves, which are then tested and shown to be infected using laboratory techniques, such as Polymerase Chain Reaction (PCR). Using canines to detect early infections could significantly help reduce disease spread in California, where HLB is currently limited to southern areas of the state and identify areas where increased psyllid control measures are needed
Who is working on the project?
Dr. Tim Gottwald, Research Leader and Epidemiologist at the USDA, U.S. Horticultural Research Laboratory in Fort Pierce, Florida, and additional collaborators with F1K9 laboratories, USDA, North Carolina State University, Texas A&M University and the California Department of Food and Agriculture.
What are the challenges and opportunities?
The volatile scent signature associated with CLas-infection settles from the canopy and simultaneously emanates from root infections pooling at the base of the tree. The detector dog interrogates the tree holistically by alerting in seconds on the scent signature regardless of its origin (i.e., a single leaf, root, stem or the entire tree if systemically infected). Conversely, other detection technologies, like PCR, are reliant on selecting and processing a small amount of tissue from large trees and often miss incipient infections because infected tissue is so rare in newly infected trees. Early detection via dogs is devoid of these sampling issues. Therefore, it is difficult to confirm CLas detections by dogs using currently available molecular or chemical detection methods. Dogs have been tested in hot and cold temperatures and with wind speeds up to 20 MPH with no perceptible degradation in detection.
Human scouts require several minutes per tree to visually examine it for symptoms, then they must collect tissue which must be transported to a diagnostic lab for processing and analysis, which is time consuming and labor-intensive. Whereas, in a residential environment dogs can assess all trees in even large yards in a couple of minutes. The major limitation to the number of trees a dog can assess per day is access to these residential properties and the time required to relocate from property to property. In commercial groves a team of two dogs and one handler can survey a 10 acre planting (~1500 trees) in 1-2 hours depending on the number of infected trees; each positive alert requires rewarding the dog and tagging the infected tree. Dogs usually work 30 min then rest 30 min and can work 6-8 hours a day.
Utilizing dogs, CLas can be detected early in a region, when it is in just a few trees. If these few early infected trees are removed, the establishment and spread of the disease could be greatly reduced.
Like every detection instrument, dogs need to be periodically recalibrated. This is done by resensitizing them to known CLas-positive trees or specially prepared ‘scent pads' that contain the scent signature of CLas to ensure they maintain > 98% accuracy of detection before being redeployed.
Funding source: This project is funded by the USDA Farm Bill, USDA HLB Multiagency Committee (MAC), and USDA ARS program funds.
This article originally posted on the Science for Citrus Health website.
Photo: Canine checking trees at Lindcove Research and Extension Center, Exeter, CA
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 https://acp-hlb2019.eventbrite.com.