(Beyond Pesticides, April 11, 2024) Scientists are moving forward in testing an agroecological method of âpush-pullâ pest management (reducing the attractiveness of the target organism and luring pest insects towards a trap) to fight the Asian citrus psyllid (ACP) in Florida orange groves, as it spreads a plant disease known as the pathogenic bacteria huanglongbing (HLB), also known as citrus greening, which is deadly to citrus trees. The disease is spread by the pathogenic bacteria Candidatus Liberibacter asiaticus (CLas). ÂThe chemical-intensive, or conventional, citrus industry is under intense pressure to find alternatives, as synthetic antibiotic use for this purpose has been successfully challenged in court.
ACP is the carrier, or vector, for HLB, spreading it through the citrus groves and killing the trees. The chemical-intensive industry has focused on using antibiotics, which the environmental and public health community has rejected because of serious medical concerns associated with life-threatening bacterial resistance to antibiotics used to protect humans. A federal district court decision in December 2023 found illegal the U.S. Environmental Protection Agencyâs (EPA) decision to register the antibiotic streptomycin in Florida citrus without adequate review of its impact on endangered species. The streptomycin lawsuit, filed in 2021 by a coalition of farmworker and public interest groups, including Beyond Pesticides, raises critical issues of antibiotic resistance, public health protection, and impacts on bees.
Organic citrus production has been on the cutting edge when it comes to managing citrus greening. Citrus farmers, growing under the USDA certified organic label, are prohibited from employing antibiotics along with other toxic pesticides.ÂOrganic growers like Uncle Mattâs in Florida discussÂthe importance of soil health that supports plant resilience, breeding programs for tolerant rootstock, the use of botanical insecticides such as neem and clove oil, and the release of the biological control agent Tamarixia wasps, which feed on Asian Citrus Psyllids.ÂWatch Uncle Mattâs Benny McClean, production manager, speak about organic citrus production in Florida at Beyond Pesticideâs 33rd National Pesticide Forum.
Similarly, Mongabay (an international environmental science nonprofit news platform) reports that those practicing agroecology, while not certified organic, are utilizing âpush-pullâ methods, using an organic plant-pheromone, methyl salicylate (oil of wintergreen), to lure pests away from citrus crops and toward âtrap cropsâ instead. The method was first developed in East Africa, and represents a more holistic and environmentally friendly approach to pest management, transitioning away from dependence on pesticides.
The âpush-pullâ pest management strategy focuses on manipulating the behavior of the psyllids to protect citrus crops by making the citrus trees less attractive while simultaneously luring ACP toward alternative, non-citrus “trap crops.” While the final results are pending, the anticipated outcome is a significant reduction in ACP populations on the treated citrus trees, thereby lowering the incidence of HLB transmission.
Methodology
An Argentinian research team, led by MarÃa Victoria Coll-Aráoz, PhD, formerly on the science faculty of the Universidad Nacional de Tucumán, studied a series of experimental plots designed to test the efficacy of the âpush-pullâ method in a real-world setting. Her research was funded under the Fulbright Scholars Program with the project title âUtilizing Plant Signaling Compounds to Manage Asian Citrus Psyllid (Diaphorina Citri), Vector of Huanglongbing Disease of Citrus.â
The three distinct test groups include:
- Control: Trees receive no treatment to serve as a baseline for comparison.
- Treated citrus only: Trees are sprayed with an organic plant hormone solution that inhibits the production of methyl salicylate, a chemical that naturally attracts psyllids.
- Treated citrus with trap crops: In addition to the treated citrus trees, this setup includes curry leaf plants (Murraya koenigii) surrounding the citrus trees. These trap crops are sprayed with methyl salicylate (a plant hormone compatible with organic systems) to make them more attractive to the psyllids than the citrus trees.
The methodological approach features two key actions simultaneously: pushing ACP away from the citrus (the “push”) and pulling them toward another target (the “pull”).
- Push: The citrus trees are sprayed with an organic plant hormone that suppresses their natural emission of methyl salicylate, a compound that attracts psyllids and other pests. Normally, when a tree becomes infected with citrus greening, the bacteria causes the tree to produce even more methyl salicylate â a positive feedback loop âdesigned by the bacteria for its own propagation,â as Dr. Coll-Aráoz explains. Reducing this methyl salicylate attractant makes the citrus trees less appealing to the psyllids and breaks this feedback loop.
- Pull: Simultaneously, the surrounding trap crops (curry leaf plants) are made more attractive by enhancing their emission of methyl salicylate, either through direct spraying of the substance or using dispensers that release the chemical, acting like perfume bottles to lure the insects.
Approaching HLBâNo cure, but manageable under organic
HLB is one of the most researched plant diseases in the current times. Hundreds of millions of dollars have been spent on research and, as The Organic Growers Guide noted in 2019, âIt is universally agreed by growers and scientists that no âsilver bulletâ has yet been discoveredâ for HLB, therefore the presence of ACP poses a severe risk to citrus crops with the potential to cause catastrophic losses. [Infected trees must be completely removed to combat this disease, as symptoms may not appear for one to two years, and a tree may succumb to HLB within five years.] Measuring between 1/6 and 1/8 inches in length, this small insect serves as the carrier for the deadly bacterium. When ACP feeds on a plant, it transmits the bacterium, which is harmless to the psyllid but causes HLB, also known as citrus greening or yellow dragon disease, in citrus and certain ornamental plants. With a one to two-month lifespan, ACP can infect an enormous number of trees by spreading the bacterium.
Most management of the HLB vector centers primarily on the intensive use of synthetic insecticides, which are prohibited from use under organic management. ACP management in conventional citrus is based largely on the intensive use of synthetic insecticides such as imidacloprid, chlorpyrifos, and dimethoate, as well as new insecticides such as cyantraniliprole. Studies have investigated the development and use of synthetic pesticides, agricultural antibiotics, and genetically engineered citrus varieties. Advocates have noted with alarm the danger of continuing to rely on highly toxic synthetic pesticides like chlorpyrifos (banned in 39 countries) and aldicarb ( banned in 100+ countries). Even Floridaâs Department of Agriculture and Consumer Services rejected state-level approval of aldicarb: âWhile there are promising new horizons for fighting citrus greening, like recent breakthroughs at UF/IFAS on genetic resistance, aldicarb poses an unacceptable risk to human, animal, and environmental health in Florida, is one of the worldâs most toxic pesticides, and is banned in more than 100 countries,â said Florida Agriculture Commissioner Nikki Fried in 2021. âThe registrantâs application does not meet the requirements of state law, and we must therefore deny the registration of aldicarb for use in the State of Florida.â In addition, concerns over using medical treatments as pesticides are not conjecture but borne out of experiences already concerning on the ground. In January 2021, EPA authorized the antibiotic streptomycin to combat citrus greening disease despite the potential for significant environmental and health risks. Critics point out that while citrus greening and cancer are serious threats, the solution should not involve repurposing critical medical treatments for widespread agricultural application, a practice that benefits corporate interests more than farmers and poses long-term public health risks.
The devastating impact of citrus greening disease has left the citrus industry in disarray, with declining production and economic losses. However, examination of available literature, unpublished research data, and grower observations have produced evidence that citrus greening may be managed and marketable fruit produced by adopting organic agricultural (and agroecological) methods, including push-pull pest control, strict disease prevention, diligent scouting, ACP control, nutritional support of healthy and infected trees, implementation of biological controls and the planting of cultivars considered âtolerantâ or âresistantâ to HLB. âPesticides havenât worked to control this vector, and weâre entering a time when these alternatives are unsustainable,â said Lukasz Stelinski, PhD, a leading entomologist at the University of Floridaâs Citrus Research And Education Center. âTheyâre too expensive. Theyâre having negative impacts in terms of insecticide resistance development, and theyâre not working.â Despite this plethora of research, there is still a dramatic underfunding of research on methods compliant with and supporting organic cultivation.
Conventional approaches relying on synthetic pesticides have proven ineffective, harmful to human health, and detrimental to the environment. Advocates say that the time has come for a transformative change in citrus farming practices, as organic citrus represents 1.5 percent of citrus acreage in the United States and three percent of the dollar valueâin other words, providing a significantly greater economic return per acre planted. Organic citrus production, supported by agroecology principles like push-pull pest management, offers a superior approach to combat citrus greening disease and revive the struggling industry. By reducing reliance on synthetic pesticides, promoting ecosystem health, and meeting the demand for organic products, organic citrus production can pave the way for a brighter future for the citrus industry.
In 2022, after yet another closure of international juice company Tropicanaâs Fort Pierce processing facility from a lack of fruit supply, plant breeder Fred Gmitter, PhD, at the University of Floridaâs land grant Citrus Research and Education Center, commented, âItâs difficult to imagine being much worse off in our industry right now. I ask this question all the time: Is this the bottom? Is this as bad as itâs going to get?â In light of Dr. Gmitter’s comments and devastating crop losses (from 200 million boxes of oranges produced in Florida in the 2000s to just 20 million boxes in Floridaâs 2023-2024 forecast), advocates urge that the current situation be viewed as a tipping point for the end of chemical-intensive, pesticide first industrial production of oranges. Florida-based national leader in organic orange juice production, Uncle Mattâs Organic, now a Certified B company, has seen growth and success and leads the way with supporting research, and practical application of organic compatible methods. For more information, please see Uncle Mattâs Benny McClean, production manager, speak about organic citrus production in Florida at Beyond Pesticideâs 33rd National Pesticide Forum.
Beyond Pesticides argues that the urgency of the existential crises that conventional Florida citrus management exemplifies can only be met with an immediate end to the use of highly toxic synthetic pesticides (including insecticides) like aldicarb, human antibiotics like streptomycin, and more. The time is now to follow what consumers already know, and a growing organic market shows that organic agriculture can overcome challenges of pest and plague to deliver nutritious food, without pesticide residue, or pesticide exposure and harm to farmers and fields, neighbors, children, wildlife, and the environment.
Our food choices directly affect the health of our environment and those who grow and harvest what we eat. Thatâs why food labeled “organic” is the right choice. In addition to serious health questions linked to actual residues of toxic pesticides on the food we eat, our food-buying decisions support or reject hazardous agricultural practices, protect farmworkers and farm families, and provide stewardship for the earth. See Beyond Pesticides for more on Eating with a Conscience. Beyond Pesticidesâ article, âThe Real Story on the Affordability of Organic Food,â lays out the hidden costs and risks of conventional, chemical-intensive agriculture, and offers helpful ideas on eating organic on a budget. To learn more about opportunities to strengthen the National Organic Program, please see the âKeeping Organic Strongâ webpage.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources
Florida growers eye agroecology solution to devastating citrus disease, Marlowe Starling, Mongabay News, April 3, 2024
Combatting Huanglongbing in Organic Systems, International Journal of Horticulture, Agriculture and Food Science (IJHAF), Cochrane, Ellen, Shade, Jessica, Jan-Feb 2019
Combatting Citrus Greening in Organic Systems A GROWERâS GUIDE, The Organic Center, January 2019
Citrus Greening: A positive outlook despite Mother Natureâs setbacks, Uncle Matt’s Organic, November 2022
Genetic Improvements Offer Best Long-term Solutions to Citrus Greening Disease, Uncle Matt’s Organic January 19, 2021
Progress Toward an Attract-and-Kill Device for Asian Citrus Psyllid Using Volatile Signatures of Citrus Infected With Huanglongbing as the Attractant, Journal of Insect Science, November 2020
