Detected in Georgia in 2002, laurel wilt’s devastating effects were observed for the first time in a Florida commercial avocado grove back in 2012. Very little was known about the disease and the ambrosia beetle that transmits it. The disease is triggered by the fungus Raffaelea lauricola that impacts the vascular system of the tree causing it to rapidly wilt. Tree mortality ranges from four to eight weeks at the onset of the pathogen’s infestation.
“Laurel wilt is an insect-disease complex, a combination of the redbay ambrosia beetle and a pathogen, which was unprecedented for the western hemisphere at the time of discovery,” said Jonathan Crane, associate director of the Tropical Research and Education Center and an Extension tropical fruit specialist for the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS).
To mitigate a novel disease has required a comprehensive approach to uncovering the layers about the beetle, the pathogen, and the disease that causes laurel wilt.
“Pursuing and conducting multidisciplinary grant research became necessary especially when you consider not only the environmental impacts that this disease could represent for the future of our Florida avocado industry, but the economic harm to our growers, the state economy, and more,” said Crane. “Coordinating efforts among plant pathologists, entomologists, epidemiologists, agricultural economists, plant physiologists and horticulture scientists have helped us look at this disease from numerous angles to find answers and control the spread.”
Here is a brief look at the most current lab work and recent findings from UF/IFAS scientists in Homestead and Gainesville.
At the fundamental level, is an interdisciplinary project funded with a five-year, $3.4M grant by the National Institute of Food and Agriculture (NIFA), a division of the U.S. Department of Agriculture (USDA), that is in its final year. The project has filled critical data gaps on laurel wilt including how ambrosia beetles inoculate the pathogen in the tree, what makes the pathogen lethal, how the tree and roots respond to the pathogen all in an effort to develop novel and cost-effective measures that will manage the disease and assess economics of control measures and their adoption by growers.
A recent EDIS publication titled Recommendations for Control and Mitigation of Laurel Wilt and Beetle Vectors in Commercial Avocado Groves, provides critical information on the recent research findings, and current recommended strategies for integrated pest management.
A key trial during the multidisciplinary project involved measuring beetle activity under varying canopies and shade levels, placing light and temperature sensors in different sections of three groves.
“We wanted to measure the level of beetle activity under different canopy management scenarios” said Daniel Carrillo, assistant professor, in the Department of Entomology and Nematology at UF/IFAS Tropical Research and Education Center. “We determined that new plantings and pruned canopies where there was less shade resulted in less beetle activity.”
A previous experiment under the same project in 2018 revealed that beetles, fly under heights of 12 feet, between the dusk hours of 4 p.m. to 8 p.m., and require non-windy conditions.
The two trials led to new canopy management recommendations for growers that have shown promising results in the search for integrated pest management methods.
Another component of the project took a deep dive to determine the vulnerabilities of avocado varieties in the United States to laurel wilt. UF/IFAS scientists looked at the anatomy and physiology of the three different botanical races of avocado based on their geographic origin: Mexican, Guatemalan and West Indian (originally from central America but brought to the West Indies). The Florida avocado belongs to the West Indian and West Indian-Guatemalan hybrid types, while others fall into the Mexican, or the Guatemalan-Mexican hybrid types.
Commercial avocadoes are propagated through grafting to maintain predictable fruit quality and quantity. This process requires combining a rootstock, the lower part of the tree that produces the roots, and a scion, typically joined at the top for producing the plant shoot and giving rise to the leaves, stems, flowers and fruit.
“We learned that the West Indian variety was generally the most vulnerable to laurel wilt,” said Bruce Schaffer, professor of plant physiology at UF/IFAS Tropical Research and Education Center. “In measuring the susceptibility of each, we learned that the scion is more vulnerable to the disease than the rootstock. Although there are general differences in susceptibility to laurel wilt among botanical races, there appears to be greater differences among varieties, regardless of race. We are continuing to search for a rootstock/scion combination that is tolerant to the disease by screening,” he added.
Meanwhile, Jeffrey Rollins, professor of plant pathology in Gainesville has taken a genetic look at the pathogen for its abilities and strengths that also help uncover weaknesses. This process required looking at the pathogen’s DNA by sequencing the genome and establishing the chromosome sequences of the fungus. The process requires finding ways to look at the pathogen by unveiling its various layers. This takes time and requires developing new approaches to uncovering those layers.
“In science we know that there is always a combination of factors that cause a disease,” said Rollins. “Here the beetle transmitting the pathogen causes a lethal disease, unlike in its native Asia where it doesn’t kill trees but has some effects on trees. My goal is to understand what makes this such an aggressive and lethal pathogen in North America.”
This fundamental work pieces apart the organism to understand it.
“In the long term, the objective is to identify genetic factors or aspects of the fungus’ metabolism, that will help us develop additional management practices or screening tools for controlling or eliminating the disease,” added Rollins.
Another critical piece of the project puzzle is an epidemiological analysis of the distribution, patterns and determinants of the laurel wilt disease and pathogen. This requires integrating information about the beetle vectors, the pathogen, the effectiveness of disease management by the grower, and the economics of decision-making about management. The objective is to understand the effects, throughout Florida and beyond, of the management options available for laurel wilt and whether growers choose to adopt them.
“Our research benefits growers by helping them understand their role in the Florida epidemic, and what level of risk their groves experience,” said Karen Garrett, a plant pathology professor based in Gainesville who is a noted expert in epidemiology and modeling technology impacts on agricultural systems.
Like COVID-19 epidemic studies, Garrett evaluates different scenarios for disease management in the region, in terms of the management choices growers have available and the growers’ decisions.
“If everyone manages well for laurel wilt, management in the region will tend to go well. Management can be expensive, however, so not everyone may manage intensively. We look at how many growers must manage well for regional management to be successful,” said Garrett.
By: Lourdes Rodriguez, 954-577-6363 office, 954-242-8439 mobile, firstname.lastname@example.org
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