UF/IFAS scientist publishes new data on insect causing lethal disease in Florida palm trees

The most important takeaway for consumers to note is that once symptoms show up on the palm tree, it is too late, which is why prevention is the first line of defense

From the University of Florida Institute of Food and Agricultural Sciences

A University of Florida scientist has published an in-depth look at the insect responsible for infecting more than a dozen species of palm trees worldwide, including the official Florida state tree, with a deadly disease known as lethal bronzing.

Homeowners, nursery managers, arborists, and landscapers now have access to the first of what will be many resources to help identify, monitor, and manage the pest and disease, which has had significant economic and aesthetic impacts on 19 palm tree species. “American palm cixiid haplaxius crudus van duzee (insecta: hemiptera: cixiidae)” made its debut this month on Ask IFAS, the University of Florida Institute of Food and Agricultural Sciences ’ Electronic Data Information Source (EDIS) peer-reviewed site.

“This first in a series of publications is an update that focuses on the insect causing the disease,” said Brian Bahder, an assistant professor at UF/IFAS.

Adults of Haplaxius crudus feeding on palm foliage, white arrow on left indicates feeding adult, with close up on right.Credit: De-fen Mou

Bahder has been leading a team of researchers studying the disease and insects. “The publication, designed for residents and industry professionals lays the foundation for identifying, monitoring, and managing the vector. As we continue to learn more about this insect, we will continue to give recommendations for how to control and how to identify it in different habitats.”

Bahder has witnessed the steady decline of palm trees throughout Florida.

The article provides a detailed description of the adult Haplaxius crudus (H. crudus) insect giving consumers a birds-eye view for identification purposes, the insect’s life cycle, the range of palm species currently reported as vulnerable to the disease, and the economic impact of the insect to the industry.

Adult Haplaxius crudus: A) dorsal view of female, B) lateral view of female, C) dorsal view of male, and D) lateral view of male; scale bar = 1mm . Credit: Brian Bahder[/caption]

One of the key takeaways to helping manage and monitor the continued spread of the species and disease is the need for consumers and professionals to sample for H. crudus.

“We have come a long way in understanding the epidemiology of this disease, and now that we know what insect is responsible for spreading it, we can start to control it,” said Bahder.

Among key research takeaways:

The current management of disease relies on tree removal and antibiotics, neither of which are sustainable, thus managing the insect will be the way to control the disease.

The first line of defense is knowing where your insect (vector) is and when it is most abundant so you can implement management options.

Identifying the insect vector is also critical; incorrect identification can result in unnecessary economic losses.

“The next phase is to optimize trapping and monitoring programs and establish different population trends in different areas of the state,” Bahder said. “We will also need to determine what insecticides will be effective and to start looking into cultural practice and non-insecticide options that may help manage vector populations both in nurseries and urban habitat.”

19 palm tree species are vulnerable

Research has identified 19 palm tree species vulnerable to the disease. Species like our state tree -- known as the sabal or cabbage palm, along with the silver date palms and the queen palms are just three of the species found to be vulnerable to the bacteria known as phytoplasma. The bacteria spread by the H. crudus feeding on the tree.

While the insects are native to Florida and the Caribbean, only a small percentage of them, -- less than 1 percent of this disease infecting population -- are found to have the phytoplasma that infects the trees.

Central Florida is home to a vast diversity of palm tree species. The disease spreads when the insect moves from one tree to another and injects infected saliva into the healthy plant.

The most important takeaway for consumers to note is that once symptoms show up on the palm tree, it is too late, which is why prevention is the first line of defense, Bahder said.

Prevention: What can be done?

Example of sampling protocol for collecting Haplaxius crudus; A) yellow sticky traps in palm canopies for adults, indicated by white arrow and B) grass/soil samples for nymphs in Berlese funnel. Credit: Brian Bahder[/caption]

Currently, the most time and cost effective method to sample for adults of H. crudus is by placing yellow sticky traps in the canopy of palms that are accessible from the ground (Figure 6). During peak adult activity, this method can capture over 300 individuals after about two weeks’ time. Adults can also be readily collected by sweep-netting palm canopies if living insects are needed. Finally, adults readily come to lights at night, so light-trapping with a mercury vapor lamp is also a useful collection method. Nymphs are far more difficult to reliably sample due to grasses covering a much large ground area than palms. Because of their cryptic habitat, yellow sticky traps, sweep netting and light trapping are not effective for sampling. Currently, the optimal strategy for collecting nymphs is by use of a Berlese funnel where clumps of grass and a thin layer of dirt/roots are dug up (Figure 6) and placed upside down inside the funnel and a light is turned on to heat the samples. As the grass dries, nymphs try to escape the light/heat and move downward, falling into a container with 95% ethanol. This method is labor intensive and not cost effective and is only recommended for specific research needs, however may be needed by nurseries in the future to supplement management programs.

As part of the palm phytoplasma diagnostic clinic at FLREC, processing of yellow sticky traps to determine presence/absence of H. crudus and if the local population carries the phytoplasma is now offered as an available service to all interested stakeholders. Sample submission forms and instructions can be found at www.bahderlab.com under the “Services” tab.

Current recommendations for management primarily involve weed/grass management in nurseries, systemic treatments of palms with dimethoate, and contact treatments against nymphs using diazinon (Howard and McCoy 1980). Both dimethoate and diazinon are commercially available. For grass management in nurseries, the current recommendation is to remove any and all grasses and replace with none monocot cover-crop. Research is ongoing to determine what chemical compounds and forumlations can be used effectively in grasses in nurseries to control populations of H. crudus.

The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human, and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state’s agricultural and natural resources industries and all Florida residents. For more details, visit ifas.ufl.edu.