Effects of Homobrassinolides on HLB-Affected Trees in Florida

Effects of Homobrassinolides on HLB-Affected Trees in Florida

By Fernando Alferez, Christopher Vincent and Tripti Vashisth

HLB

In the current scenario of widespread infection and severe symptoms of HLB in Florida, horticultural practices that improve plant health in the presence of the disease are needed. For this reason, we sought to follow up on reports of positive effects of a brassinosteroid on infected plants. Brassinosteroids are a relatively newly discovered group of plant hormones that regulate multiple developmental and physiological processes. Most interestingly, brassinosteroids induce disease resistance in a great number of crop plants against bacteria, fungi, oomycetes and viruses. Brassinosteroids are present in two active forms, epibrassinolide (EBL) and homobrassinolide (HBr).

Recently, EBL was shown to reduce Candidatus Liberibacter asiaticus (CLas) bacterial titer and alleviate symptoms of HLB in mature citrus trees in Cuba. The results of the Cuban study, over a 12-month period, were impressive: In a greenhouse trial, bacterial titers were reduced to non-detectable levels. In the field, a seven-fold reduction of bacterial titer was measured.

HLB

This effect seems to be mediated by the activation of a large number of defense-related pathways in the tree. However, the long-term effects of this treatment on tree health and fruit yield and quality were not assessed.

HBr is commercially available in the United States and has been proven effective in increasing resistance to disease in other plants such as tobacco and apple. Hence, there is an opportunity for testing HBr in citrus trees grown in Florida under HLB-prevalent conditions.

A research project, funded by the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research Initiative, started in December 2017 with the overall goal of assessing effects of HBr on citrus tree health, fruit yield and quality. The project also includes assessing CLas bacteria titer in the central and southern citrus-producing regions of Florida to ensure that results are applicable statewide. Researchers are conducting experiments in groves in Lake Alfred at the Citrus Research and Education Center and in Immokalee at the Southwest Florida Research and Education Center (SWFREC) using the same varieties (6- to 8-year-old Valencia trees on Swingle rootstock) and experimental design.

Starting in December, spray treatments were performed every two weeks for six months at both locations, following the dosage and frequency published in the Cuban study. Treatments were: 1) water (control), 2) 0.084 micrometer (μM) HBr and 3) 1 μM HBr. Fruit detachment force (FDF), fruit drop and fruit peel coloration were tested. Leaves were collected from every individual tree monthly to measure bacterial population. Timing of flushing and blooming in treated trees was also assessed. Canopy volume, trunk diameter and leaf chlorophyll content in new, fully expanded leaves were examined as well.

Although the experiment is still in its first year, we can report on certain trends in tree health, fruit yield and quality. The treated plants must be followed further before recommendations can be made to Florida growers.

BACTERIAL POPULATION
Bacterial population was assessed monthly by real-time polymerase chain reaction according to U.S. Department of Agriculture Animal and Plant Health Inspection Service recommendations. Prior to the start of the experiment, all trees were HLB positive. After six months, no significant differences were observed between control trees and trees that received HBr.

HLB

TREE PHENOLOGY
Chlorophyll content was evaluated non-destructively at two different times after the first application in December: 1) in March, after new leaves were fully expanded and 2) in May, when these same leaves were mature. Data show that chlorophyll content was significantly higher in leaves from both HBr treatments, and these differences increased with time (Figures 1A and 1B). There were no differences in canopy volume and trunk diameter among different treatments, though it is likely that six months is too early in the course of the study to find whole-plant differences.

HLB

Noticeably, we found that blooming occurred 10 days earlier in HBr-treated trees (irrespective of the dosage) as compared to the non-treated trees, and flowering was profuse and uniform (Figure 1C). These effects were more pronounced in trees at the SWFREC experimental site. Trees showed denser and darker-green canopies after the June flush when compared to the beginning of the experiment (Figures 1C and 1D).

FRUIT YIELD AND QUALITY
Color measurements were taken monthly using a portable Minolta color meter. Color break and development occurred earlier in trees treated with HBr at both concentrations compared with untreated trees (Figure 2). This effect disappeared over time and by the end of maturation (May 25, 2018). There were no significant differences in fruit coloration.

HLB

HLB

FDF was higher at higher HBr concentrations in March and early May (Figure 3). Total fruit yield at the end of the experiment was higher in trees treated with higher HBr concentration (242.5 pounds) compared with trees treated with the lower concentration (210.1 pounds) and with water controls (191.7 pounds). Average fruit weight and diameter increased significantly in response to the higher HBr concentration (Figure 4). The higher retention force of the fruit to the tree may explain the increase in yield at the end of the experiment.

HLB

CONCLUSIONS
The effects observed after the treatments with HBr were not what we initially expected, as we were more interested in assessing reduction in bacterial infection in the citrus trees. However, we observed advanced blooming date and acceleration of fruit maturation. Trends regarding tree health, fruit yield and quality observed after HBr treatments are worth following.

Determining appropriate timing of product application may allow HBr to be used as a new management tool for Florida citrus growers. The lack of effect on bacterial population could be due to the fact that the study is still in its early stage. Nevertheless, results from our study suggest that HBr treatment may improve tree health and, therefore, tolerance and productivity of infected trees. The study will continue for an additional year to investigate whether homobrassinolide applications are a suitable management practice to combat HLB.

Acknowledgements: This research was funded by the UF/IFAS Citrus Research Initiative. The HBr used in this study was a gift from Repar, Inc. in Maryland. Thank you to the HLB Detection Laboratory at the SWFREC for diligent analysis of samples.

Fernando Alferez, Christopher Vincent and Tripti Vashisth are UF/IFAS assistant professors.

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Lemons In Florida

Lemons: What’s Available and What’s Coming

lemons

Lemon varieties now available for planting in Florida and varieties that may be available in the future were discussed at a recent lemon workshop in Lake Alfred. Fred Gmitter, a University of Florida Institute of Food and Agricultural Sciences researcher, summarizes his presentation.

“The currently available varieties are Bearss and Eureka,” Gmitter says. “Bearss is a heavy-bearing tree; it produces more juice. Eureka is perhaps slightly better for the fresh market. It looks better; it’s a larger size.”

“We had a project going in Florida for many years to develop lemons that produce more oil,” Gmitter adds. “The oil is really perhaps the most valuable commodity” coming from lemons. But, he adds, “We were working on lemons at a time when very few people in Florida were interested in lemons.”

Gmitter’s work on lemons for peel oil was supported by a major beverage company interested in obtaining sustainable amounts of oil. The researcher says his team developed lemon selections that produced up to 40 percent more peel oil per fruit than ordinary lemons. He reports there is a trial in Bolivia of 43 top lemon selections for peel oil on 200-plus acres. The 43 selections were chosen in Florida from more than 4,200 individual trees.

In Florida, the researchers selected the three highest yielding cultivars for oil. “We have patent applications in for those three, and they will be available to Florida growers anytime soon,” Gmitter says.

 

How to Handle Glyphosate-Related Fruit Drop

glyphosate

By Ramdas Kanissery, Fernando Alferez and Ozgur Batuman

Herbicides are one of the key inputs necessary for effective management of a wide diversity of weed infestations in citrus crop production. Most weeds in citrus could be controlled by adopting a weed management program that utilizes a combination of herbicides based on their selectivity and compatibility with the crop. This would be considered more cost-effective than present mechanical and cultural methods of weed management.

After introduction in the 1970s, glyphosate (example trade name: Roundup), became very popular among citrus growers for its broad-spectrum weed control under trees and in row middles. The use of glyphosate as a “burn-down” application, alone or in combination with other herbicides, became a standard practice in citrus groves.

Glyphosate, because of its non-selectivity and relatively low cost, is used extensively for post-emergent weed management in Florida citrus. A National Agricultural Statistics Service report from 2010 reveals that 72 percent of orange and 63 percent of grapefruit groves received glyphosate treatments, underscoring the importance of glyphosate as a major herbicide option for citrus growers.

Glyphosate, with its broad-spectrum of activity, is very effective at controlling a wide range of weeds, but many recent scientific reports suggest a relationship between extensive glyphosate application and adverse impacts on non-target plants. As glyphosate use has increased in various crop production systems, several concerns have arisen associated with this herbicide’s interaction with available nutrients, phytotoxicity and passive effects on plant pathogens.

Chief among these concerns are: 1) increased crop sensitivity to diseases, 2) reduced availability of micronutrients to crops through chelation and 3) inhibition of root growth. As citrus weed management programs have continued to rely more heavily on glyphosate, the occurrence of citrus fruit drop resulting from glyphosate application has become an increasing grower concern over the years.

GLYPHOSATE CONTACT WITH CITRUS
Glyphosate-related fruit drop usually occurs in fall and coincides with the application of glyphosate in late summer/early fall in early-season citrus varieties. Some research reports have suggested that susceptibility of fruit to glyphosate increases as it nears maturity. In one such study by D.P.H. Tucker in 1977, glyphosate sprayed on 6-week-old citrus fruit did not show damage and drop. However, when the herbicide came in contact with 5-month-old fruit, extensive drop was observed. As fruit develops, especially on younger trees, heavy fruit-bearing or low-lying branches are more likely to come in contact with sprayed herbicides, resulting in glyphosate contact with the fruit.

There are several potential routes through which glyphosate can enter the citrus tree, including absorption through leaves and other green or woody tissues following contact with spray and root uptake from the soil. Only fruit that comes in direct contact with the glyphosate spray during the susceptible period may be subject to glyphosate-related fruit drop. Also, glyphosate residues persisting in the soil are available for root uptake by the trees. Glyphosate is found to accumulate in the soil and the plant tissues. Hence, recurring applications add cumulatively to previous doses, and such increasing concentrations may pose problems in future years.

The exact reason behind the glyphosate-linked fruit drop is not known. However, glyphosate has been shown to enhance ethylene production in plant tissues. Ethylene is known to induce leaf and fruit abscission in maturing citrus. Possibly, exposure of maturing citrus fruit to glyphosate could result in elevated concentrations of ethylene and consequent fruit drop.

glyphosate

MORE GLYPHOSATE MEANS MORE DROP
One indicator of fruit drop is reduction in fruit detachment force (FDF), the force necessary to detach a fruit from the bearing branch, resulting in drop. Preliminary studies conducted at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Southwest Florida Research and Education Center show that FDF is affected by glyphosate in a dose-dependent manner. FDF is reduced considerably when glyphosate is applied at higher rates (Figure 1), indicating that higher doses of glyphosate are more likely to induce fruit drop.

The objective of this study was to determine the effect of glyphosate dosage on the abscission of mature citrus fruits. Six-year-old trees of Valencia grafted onto Swingle rootstock received glyphosate (Round-up Power MAX) application at three rates in the summer of 2017.

Glyphosate was applied with a tractor-mounted spray boom under the trees (in the rows). The treatments included a low rate (22 ounces per acre, one time), medium rate (55 ounces per acre, 2 times) and a high rate (110 ounces per acre, five times) of the herbicide. Water was sprayed from the herbicide boom in the control plots. The mature fruits were collected from the lower third and upper third portions of the tree at weekly intervals to assess the FDF with a pull force gauge. The observed reduction in the fruit detachment force suggests an increased chance for fruit drop.

MANAGEMENT METHODS
There are some ways growers can manage herbicide-related fruit drop. The following methods are recommended.

Maintain a Safe Sprayer Distance 
Maintaining a safe distance between the sprayer boom and the tree while spraying herbicide is essential to avoid any potential spray contact with the tree. The herbicide boom should be adequately below the tree canopy to avoid contact with fruit. The boom must still be high enough to pass over the weeds for exposure to the herbicide spray.

Mechanical damage from herbicide applicators as a cause of fruit drop is often overlooked by growers. Hitting the tree trunks with the herbicide boom will result in knocking down the fruit and hence should be avoided. Additionally, scratching on the tree trunk during herbicide application will expose the trees to chemicals and pests.

Position the Off-Center Nozzle Correctly
The off-center (OC) nozzle is at the terminal end of the herbicide boom. Nozzle angle determines whether the herbicide application is directed upward and toward the tree trunk, foliage or fruit or downward at the intended weeds targeted. Optimal placement of the OC nozzle will minimize herbicide drift into the trees and prevent applying the herbicide directly to the tree. The greater the nozzle angle, the higher and further beyond the end of the boom the spray is directed, and the greater the chances for herbicide contact to occur in the tree canopy.

Even a closed OC nozzle may help to curb the glyphosate-related fruit drop. Properly adjusted spray booms and well positioned OC nozzles can be used during the sensitive periods near fruit maturity to reduce fruit drop from direct spray contact.

For more information on herbicide application best management practices in citrus, see http://edis.ifas.ufl.edu/ae246.

Skirt Citrus Trees
Skirting or raising the tree skirts is another way to prevent herbicide spray contact with the foliage and fruits. Skirting is the process of pruning the low-hanging branches and limbs of the trees. This allows easy movement of herbicide spray booms and thus enables uniform herbicide application under the tree canopy and less contact with the foliage and fruits.

CONCLUSION
Assuring good yield from citrus starts with preventing unnatural fruit drop of young fruit. The herbicide glyphosate is linked to the loss of maturing fruit in citrus. Improper spray applications directed toward the tree canopy will result in herbicide contact with citrus fruits and immature fruit drop. Maintaining a safe spray boom distance and careful positioning of the angle of OC nozzles during the sensitive period near fruit maturity will help to reduce fruit drop from direct spray contact.

Ramdas Kanissery, Fernando Alferez and Ozgur Batuman are assistant professors at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.

New podcast launched for citrus producers 

The University of Florida Institute of Food and Agricultural Sciences and Southeast AgNet are partnering to provide the latest news on citrus-related research in a monthly podcast.

 

The podcast, “All in for Citrus,” will launch the last week in September and will feature short interviews with scientists working to find solutions to citrus greening and other devastating citrus diseases.

“This is the latest tactic in a comprehensive communications effort launched this past summer by the UF/IFAS Citrus Team,” Michael Rogers, director of the UF/IFAS Citrus Research and Education Center in Lake Alfred, Fla., said in a news release.

The podcast complements the new website, citrusresearch.ifas.ufl.edu, and a new monthly newsletter, according to the release.

Sugar Belle/Rootstock Interaction

Florida citrus growers recognize the Sugar Belle® mandarin hybrid for its tolerance of citrus greening disease, and new findings from the University of Florida Institute of Food and Agricultural Sciences suggest that rootstock selection may play a role in keeping Sugar Belle® trees productive even if they become infected with the bacterial malady.

“We now have proof of concept that, in Sugar Belle®, rootstock selection has an effect on the tree’s metabolism,” said plant pathologist Nabil Killiny, a UF/IFAS associate professor and lead researcher in the study. “It is likely that growers can optimize the productivity of Sugar Belle® trees with the right rootstock selection, and we have studies planned that will investigate this question.”

The research thus far has not involved trees already stricken with greening disease, also known by the Chinese term Huanglongbing or the acronym HLB. Studies on infected trees will be a future step in evaluating rootstock options for Sugar Belle®, Killiny said.

Developed by UF/IFAS citrus breeders and released in 2009, Sugar Belle® has proved to be more tolerant of HLB than most citrus varieties grown commercially in Florida, said Killiny, based at the UF/IFAS Citrus Research and Education Center in Lake Alfred. The disease is caused by an invasive bacterium that is transmitted by an invasive insect, the Asian citrus psyllid. HLB was first reported in Florida in late 2005 and subsequently spread statewide, drastically reducing yields.

The current study, published earlier this year in the journal “Plant Signaling & Behavior,” showed that metabolic activity in three groups of healthy Sugar Belle® trees differed, depending on the rootstock used. As with most commercial citrus in Florida, trees used in the study consisted of two sections grafted together – a hardy root system, or rootstock, topped with a highly productive above-ground section known as a “scion” of a different variety – in this case, Sugar Belle®.

“We deliberately focused the study on Sugar Belle® trees that used three of the most popular rootstocks – Swingle citrumelo, Carrizo citrange and UF-15,” Killiny said.

In the study, researchers purchased one-year-old Sugar Belle® trees from nurseries, acquiring 12 trees with each of the three rootstocks investigated. After acclimating the trees to greenhouse conditions for one month, the team took leaf samples from each tree, analyzing them with gas chromatography-mass spectrometry instruments to detect organic chemicals associated with plant growth and defense.

Results from the analyses showed that the overall chemical profiles obtained from the samples varied significantly depending on the rootstock used.

Although trees used in the study were not infected with HLB, Killiny notes that Sugar Belle® trees with Swingle citrumelo rootstock produced the greatest amounts of two compounds known to have antimicrobial effects, quinic acid and ferulic acid. Consequently, it appears likely that Sugar Belle® will tolerate HLB best when grown on Swingle citrumelo, because the two acids would probably limit the bacterial population, or titer, in an infected tree. These results led the team to conclude that, among the three rootstocks tested, Swingle citrumelo is probably the best choice for optimizing greening tolerance in Sugar Belle®.

“Our next step is to analyze Sugar Belle® on 12 different rootstocks,” he said. “From there, we hope to develop recommendations for growers that will ensure the best possible performance from Sugar Belle® trees.”

Funding for this study was provided by a $75,000 grant from the federal Citrus Disease Research and Extension program, which was authorized by the 2014 federal Farm Bill and administered by the U.S. Department of Agriculture through its Specialty Crop Research Initiative.

By: Tom Nordlie, 352-273-3567, tnordlie@ufl.edu

Lemons in Florida

Lemons in Florida: Something New Under the Sun?

lemons

By Fred Gmitter, Bill Castle and Jude Grosser

King Solomon once pointed out that “there is nothing new under the sun,” meaning that what has happened before will happen again. Although the idea of growing lemons in Florida is viewed by some these days as a new thing, Florida actually has a fairly long history of lemon production.

FLORIDA LEMON HISTORY
Lemons were a part of the Florida landscape in the late 1800s and were seen as a potentially competitive fresh fruit commodity against the newly developing California lemon business, because of proximity to the eastern U.S. marketplace. There were some production problems in the Florida environment, but there still was optimism that growers could make a go of it. It was a viable plan until Dec. 29, 1894, when the first of two “Great Freezes” struck the state. If there was any hope for lemons after the first freeze, a second even colder wave of Artic air came through Florida on Feb. 9, 1895. In less than five weeks, Florida’s dream of growing lemons was put to rest for the next several decades, as the state’s citrus industry learned that cold is a serious limiting factor for lemon production.

Lemons mostly languished as a fresh fruit option for Florida growers until the late 1950s and 1960s. In 1958, a series of articles was published, led by former Citrus Research and Education Center (CREC) Director Herman Reitz. He described the beginning of the latest craze in Florida citrus: planting lemons for processing into lemonade! L.C. Knorr of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Experiment Station (as CREC was called then) in Lake Alfred reported 3,000 acres of lemons in Florida. By 1972, Robert C.J. Koo, also from CREC, reported that there were some 8,760 acres of lemons in the state.

There was some effort to produce fresh lemons near West Palm Beach, on macrophylla rootstock, but costly tree maintenance requirements and a small and elusive window in the marketplace dominated by California meant profitability also was elusive. But major companies such as Minute Maid and Libby, McNeil and Libby were players in the processed lemon game.

Variety trials were planted that included up to 40 different selections in Avon Park and Indiantown. These trials served as sources of fruit for experiments and budwood for nursery propagations. Minute Maid planted substantial acreage of Bearss lemon on rough lemon rootstock in Indiantown, and Libby had lemons at several locations. But, once again, Artic air put a quick end to the lemon business in Florida with the multiple freezes of the 1980s. Aside from a few modest plantings targeting niche markets, lemons in Florida languished again.

Fast forward to 2014 and 2015, when the Florida citrus business was experiencing its greatest existential threat, huanglongbing (HLB). Production was declining precipitously everywhere in the state. Growers, many of them of multigenerational lineages, were dropping out of the business, like the Hamlin oranges were dropping off of the trees because of HLB. Grapefruit production from the Indian River area declined at an even faster rate than did orange and other specialty fresh fruit types.

Juice processing plants that formerly would run almost non-stop from late November through early June, now were closing for weeks at a time. Truck yards that once were full of dozens and dozens of trailers waiting to dump their fruit loads, then go out and load up again, were now more empty than full of cargo. Simultaneously, contemporary consumers were turning away from orange juice as the signature breakfast drink of generations. Supply was down, demand was down, but the ever-resilient Florida citrus industry began to look for another way to survive and be profitable. And once again, lemons came back into the sun.

TODAY’S DIVERSE LEMON USES
Why lemons now? What hope do they provide? Haven’t we learned from the perspective of historical cold events? Is there something new under the sun?

The lemon is a fruit with diverse uses. It can be grown for the fresh market, as it is in most places worldwide, or for processing into juice and various other products. Economists who monitor the marketplace tell us that one of the few types of citrus beverages for which consumer demand is increasing significantly is lemonade and similar drinks. The idle Florida juice processing facilities potentially could be more active, and therefore more profitable, if they had lemons as raw product for processing, especially given the lack of oranges for juicing.

In addition to juice, lemon peel oil is a very valuable byproduct commodity. Many of the world’s soft drink products are flavor-enhanced with a drop of some part of the essence of the lemon oil. Lemon oil is commonly used in many personal care and cleaning products, and lemon fragrances are also important to the food industry for flavoring a wide range of products. The white portion of the lemon peel, the albedo, is a rich and highly desired source of pectin that has many uses in the dairy, confectionary and healthcare industries. Thus, growing lemons is appealing because of its multiple uses and its noted greater tolerance of HLB.

PRODUCTION PROS AND CONS
However, growing lemons is a bit more challenging than growing other citrus varieties mostly because of the growth and fruiting habits. Lemon trees are vigorous and thorny. The latter is no small consideration because of harvesting and extra costs generated by special approaches associated with wiry, thorny trees.

Despite Florida’s repeated experience with growing lemons, it has been hard to avoid the need to relearn the knowledge and tricks needed to produce this fruit. Nevertheless, there is excitement in the air about lemons because they are HLB-tolerant, fast-growing and precocious. Thus, commercial production begins early. If grown for the processing market, there are several options for use of the fruit, all with good income potential. Also, management of a juice-fruit grove is likely more forgiving when it comes to cultural and harvesting costs and practices.

But what of the cold sensitivity of the lemon trees that has spelled disaster many times before? Lemons can be quite cold tolerant, but only if they have the opportunity for good cold acclimation. Such conditions in the widely fluctuating Florida winter climate do not really exist. We cannot say that the threat is not real, despite the increasing average annual temperatures. There still can and will be those few very cold nights. But there are some things to keep in mind about this threat as well.

The serious freeze events that killed lemon groves in the past generally took place before the widespread use of microirrigation systems to weather through the freezes. So, when there are severe cold events in the future, it may be possible for growers to keep at least the trunk and main scaffold limbs alive. If microirrigation succeeds, then the inherent vigor of the lemon tree can regrow new productive canopy faster than probably any other type of citrus tree. For example, the Argentine lemon industry in Tucuman suffered great losses just a few years ago to uncommonly severe freezing, only to see production quickly rebound a mere two seasons later. The lemon crop in Florida would be harvested generally before the coldest times of the year.

ADVANCES IN LEMON BREEDING
One of the lesser known aspects of the UF/IFAS CREC citrus breeding program has been a project to develop new true lemon cultivars that will produce greater quantities of the “liquid gold” that is lemon peel oil. Researchers planted more than 4,000 new lemon clones developed using the same approaches that were successfully used for sweet orange improvement. They measured peel oil production in the Florida environment annually. The goal was to find lemon varieties that had consistently high oil yields, exceeding 8 kilograms per metric ton.

lemons

They succeeded in finding more than a dozen that averaged well over this threshold across at least five seasons of data collection (see graph). These new varieties have been approved for release, and the top three soon will be made available to Florida citrus growers. In addition, a nearly seedless clone will also be released for Florida growers who have interest in the fresh option.

Lemons can be grown more cheaply in other parts of the world, and their concentrated juice can be shipped globally. But when the economic benefits and value of the peel oil are factored in, it begins to seem more plausible for this old crop to be grown profitably once again under the Florida sun. The UF/IFAS broadly targeted citrus breeding program may once again contribute to the suite of options available to the Florida citrus industry to continue to thrive.

Fred Gmitter and Jude Grosser are professors, and Bill Castle is an emeritus professor, all at the UF/IFAS CREC in Lake Alfred.

Fungus to Target Asian Citrus Psyllid

Scientists Set to See if Fungus Can Stop Asian Citrus Psyllid

Fighting plant disease with jet blast sprays is standard practice for Florida citrus growers fighting Asian citrus psyllid — the vaunted vector of  citrus greening. But, to spray a fungus to control a single insect that carries a disease-causing pathogen is uncommon. With that, scientists from UF/IFAS and the Florida Research Center for Agricultural Sustainability are collaborating to test an insect-killing fungus applied with horticultural oil sprays in a Vero Beach, FL, citrus grove.

Pasco Avery, a Biological Scientist based at IRREC, tested the fungus against the psyllid under laboratory conditions. His findings, which are published in Insects, Biocontrol Science and Technology as well as Florida Entomologist, document the fungus’ promise as an effective biological control agent against the Asian citrus psyllid.

According to Avery, the fungus kills the psyllid but is compatible with beneficial insects like lady beetles, lacewings and parasitic wasps. “The fungus is not a panacea, but it is expected to greatly reduce the problem we have in managing the psyllid populations.”

Bob Adair, Executive Director at the Florida Research Center for Agricultural Sustainability, heard about Avery’s work with the fungus and approached him about using commercial sprayers to distribute the fungus in his groves. Adair has partnered with UF/IFAS on multiple occasions over the years to conduct agricultural research.

Avery carried out experiments in his lab to determine if the oils were compatible with the fungus. He found the oils sustained the fungus and helped it to grow and thrive, he said.

Adair said the next step was to determine its efficacy in field trials in citrus groves. The fungus needs to be tested in outdoor groves to determine whether it can suppress the Asian citrus psyllid population to the point where trees will be protected and that the psyllid will not become resistant to the sprays.

Avery and Adair conducted a first field spray trial in mid-June. About 1 acre of trees was sprayed on one side of the row. The scientists mixed 1% of a commercial product containing I. fumosorosea with stylet oil for 65 pounds of spray. The spray was applied to the trees at dusk with a pull air blast sprayer hitched to a tractor.

Avery said the fungus was effective in suppressing the psyllid population and that it lasted for up to 14 days after application. “What we found with this first experiment was that the fungus was as effective as the active ingredient of the insecticide spinosad,” Adair exclaimed.

A second field trial is scheduled for September. For that trial, both sides of the trees in the same grove will be sprayed with fungus added to the horticultural oil.