Citrus greening symptoms

Development of an Automated Delivery System for Therapeutic Materials to Treat HLB-infected Citrus (Citrus Greening Disease)

Louise Ferguson, a Cooperative Extension Specialist in the Department of Plant Sciences at UC Davis and with UC Cooperative Extension, is a Co-PI in a $3.4 million USDA NIFA-funded project, “Development of an automated delivery system for therapeutic materials to treat HLB-infected citrus.”

The four-year project is based at University of Florida, UC Davis/UC Cooperative Extension, and Texas A&M. The researchers are developing a new automated technology that will homogeneously deliver bactericides into the vascular system of citrus, through numerous tiny punctures in the tree trunk and scaffold branches. The bactericides will then be transported through the tree’s hydraulic conducting system.

The goal is to determine time and season that are most suitable for effective delivery and distribution of bactericides in citrus to control HLB (Huanglongbing, or Citrus Greening Disease) and improve tree health and productivity.

Candidatus Liberibacter asiaticus is the bacterium that is associated with the most serious citrus disease, HLB. In most countries affected by HLB, the bacterium is vectored by the Asian citrus psyllid (ACP), Diaphorina citri. Worldwide, ACP and HLB have spread to most citrus growing regions.

Asian citrus psyllid. (photo Univ. of Florida)


In the U.S., the disease threatens the future of Florida’s annual $9 billion industry and the pathogen and vector are continuously spreading in other major production areas in Texas and California. Citrus growers in Florida are investing heavily in nutritional, insecticide, and bactericide programs with limited success. With the devastating impacts of HLB on the citrus industry and no viable treatment options identified, growers are seeking alternative solutions to reduce the bacterium levels in trees and prevent HLB-induced decline. Since the first detection of HLB in 2005 in Florida, citrus production cost per acre has substantially increased from approximately $900 to $2,200 and continuation of management at this level is not sustainable.

Leaves with huanglongbing symptoms. Mottling and yellowing of foliage that crosses leaf veins is a symptom. (photo UC ANR)


As of July 2018, 774 citrus trees in three southern California counties were removed after testing positive for the disease. State officials also collected 190 HLB-positive Asian citrus psyllid (ACP) samples from these locations. The ACP insect is the only known vector responsible for spreading the disease from tree to tree. Once a tree has the disease it is believed to be incurable.

While California has not suffered the devastating 60 percent production loss Florida is experiencing, the California industry is preparing for the worst. As of July 2018 there were no reports of HLB in commercial orchards in California.

The climates of California and Florida differ as do the citrus cultivars. Florida’s hot humid climate and sandy soils produce the sweet, high-juice content oranges preferred for juice. California’s Mediterranean climate produces fresh-eating Navel and Mandarin and lemons, with lower juice and sugar content.

“The spread of the insect vector and disease may differ due to climate and cultivar,” noted Ferguson. “However, with California’s $7.1 billion citrus industry, and in light of Florida’s rapid citrus decline from HLB, we cannot assume California will not experience a similar decline.”

Among the urgent research priorities identified were strategies for using bactericide to rehabilitate declining trees; specifically, development of novel application technologies to improve uptake of therapeutic materials including bactericides for HLB management.

The project will focus on developing an automated delivery system that addresses the need for non-conventional, economically viable and sustainable application technologies for HLB management. The primary goal is to develop a practical delivery device that growers can install on existing equipment for applying therapeutics to citrus trees. In the long-term, this system can be designed for adaptation to other disease and pest control applications.

Example of the Automated Delivery System (ADS) mounted on an ATV, next to a model of a citrus tree. (image from NIFA research proposal.)


The major outreach/extension effort is being led by Project Director and Professor Ozgur Batuman (University of Florida) and Co-PIs Louise Ferguson (UC Davis/UC ANR) and Veronica Ancona (Texas A&M), and will focus on communicating the project’s progress to growers and other stakeholders.

“After working with the Florida and Texas cooperators in evaluating the project’s results,” said Ferguson, “I will develop the extension education program for California’s citrus scientists and industry, in conjunction with UC Cooperative Extension farm advisors.” Ferguson’s primary expertise is the production physiology of pistachios, olives, citrus, figs, persimmons, and pomegranates.

Extension and outreach communication through a website, field days, grower seminars, presentations, flyers, published articles, handouts, emails, social media, and other means will keep growers and state regulators aware of the progress of the project and educate growers about the automated delivery technology and its application in citrus. Grower/consumer meetings and education sessions will be prepared to educate communities about the new technology and benefits to the citrus industry. Special programs will be developed to educate the public and increase acceptance of fruit and juice produced with this technology.


(Article by Ann Filmer, Plant Sciences, UC Davis.)

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