New Technology Targets Citrus Greening Disease

By Ann Filmer

Louise Ferguson, a Cooperative Extension Specialist in the Department of Plant Sciences at UC Davis and with UC Cooperative Extension, is co-principal investigator in a new $3.4 million project funded by the U.S. Department of Agriculture’s National Institute of Food and Agriculture, “Development of an automated delivery system for therapeutic materials to treat HLB-infected citrus.”

The four-year project is based at University of Florida, with collaborators at UC Davis/UC Cooperative Extension and Texas A&M University. The researchers are developing a new automated technology to deliver bactericides into the vascular system of citrus trees 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 University of Florida, UC Davis and Texas A&M are working on technology to deliver bactericides to citrus trees to control citrus greening disease (Huanglongbing or HLB). The vehicle-mounted device will inject bactericides through tiny puncture holes in the trunk and branches.

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

Citrus greening is caused by the bacterium Candidatus Liberibacter asiaticus. In most countries affected by HLB, the bacterium is spread by an insect, the Asian citrus psyllid, Diaphorina citri. The 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.The disease has spread to most citrus-growing regions worldwide.

In the U.S., the disease threatens the future of Florida’s annual $9 billion industry and the pathogen and vector are 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, an unsustainable cost.

As of July 27, 2018, 774 citrus trees in the three southern California counties were removed after testing positive for the disease. State officials also collected 190 HLB-positive Asian citrus psyllid samples from these locations.

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.

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,” Ferguson said. “However, with California’s $17 billion citrus industry, in light of Florida’s rapid decline from HLB, we cannot assume California will not experience a similar decline.”

Novel application technologies

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.

The major outreach/extension effort is being led by project director Professor Ozgur Batuman in Florida, Ferguson at UC Davis 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 this 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, which will be administrated through a website that will include results of this work.

More information

Fresh Citrus at Risk From Devastating Disease (UC Davis News)

Targeting the Asian Citrus Psyllid (UC ANR)

Ann Filmer is communications director for the UC Davis Department of Plant Sciences

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