{"id":545767,"date":"2025-04-15T17:41:26","date_gmt":"2025-04-15T20:41:26","guid":{"rendered":"https:\/\/revistapesquisa.fapesp.br\/?p=545767"},"modified":"2025-04-15T17:41:26","modified_gmt":"2025-04-15T20:41:26","slug":"new-cultivation-techniques-seek-to-curb-the-spread-of-citrus-disease","status":"publish","type":"post","link":"https:\/\/revistapesquisa.fapesp.br\/en\/new-cultivation-techniques-seek-to-curb-the-spread-of-citrus-disease\/","title":{"rendered":"New cultivation techniques seek to curb the spread of citrus disease"},"content":{"rendered":"
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FUNDECITRUS<\/span>Psyllids (seen hanging above<\/em>) pick up or spread bacteria as they feed on tree sapFUNDECITRUS<\/span><\/p><\/div>\n

In a destructive alliance, a group of bacteria and a group of insects\u2014one causing and the other spreading citrus greening, one of the most devastating diseases in citrus farming\u2014have continued to torment orange, tangerine, and lemon growers in Brazil. A combination of pest outbreaks, severe droughts, and erratic rainfall has stunted fruit growth and led to a 25% reduction in citrus output in S\u00e3o Paulo and Minas Gerais compared to 2023, according to a May report from the Brazilian Fund for Citrus Protection (FUNDECITRUS). As a consequence, orange prices have surged by an average of 40% in markets and produce stands.<\/p>\n

Since the disease was first detected in 2004 in S\u00e3o Paulo\u2014and later in Minas Gerais, Paran\u00e1, Mato Grosso do Sul, Santa Catarina, and most recently in Goi\u00e1s this June\u2014citrus greening has resulted in the removal of approximately 60 million trees, which represents 23% of the 260 million orange and other citrus trees grown in the country. Most of these are concentrated in S\u00e3o Paulo, which accounts for about 75% of the country\u2019s citrus output.<\/p>\n

In Brazil, citrus greening is caused by two species of bacteria: Candidatus<\/em> and Liberibacter<\/em>. Small, grayish insects up to 2 millimeters long, known as Asian citrus psyllids (Diaphorina citri<\/em>), pick up the bacteria while feeding on sap from infected plants and spread it to healthy ones. The bacteria can infest the phloem (the vascular tissue that transports nutrients, such as amino acids and sugars) of all citrus species (including oranges, tangerines, mandarins, limes, and lemons) and even other plants, like orange jasmine (Murraya paniculata<\/em>), which is popular in landscaping. Following their discovery in 1942 in Brazil, psyllids were initially considered a minor and mostly harmless citrus pest\u2014until the arrival of the bacteria responsible for citrus greening.<\/p>\n

Also known as huanglongbing (HLB), meaning \u201cyellow dragon disease\u201d in Chinese because of the yellow leaves on infected branches, citrus greening has proven even harder to fight than the previous major citrus pest, citrus variegated chlorosis (CVC), caused by the bacterium Xylella fastidiosa<\/em>\u2014the landmark genome sequencing of the Xylella<\/em> bacterium kickstarted the FAPESP Genome Program in 1997 (see<\/em> Pesquisa FAPESP issue n\u00b0 184<\/em><\/a>). Xylella<\/em> spreads slowly in the xylem (the tissue responsible for transporting water and nutrients, located closer to the outer layers of the plant than the phloem), and its vectors, the glassy-winged sharpshooters, spread less aggressively than psyllids do.<\/p>\n

CVC has now been brought under control. \u201cWe developed a system for growing seedlings in screened nurseries, implemented new disease control methods and vector management strategies, and saw the incidence rate drop from 40% in the early 2000s to less than 0.5% today,\u201d explains Juliano Ayres, a crop scientist and general manager at FUNDECITRUS. When citrus greening arrived in Brazil, growers tried to use the same tactics that worked against CVC\u2014controlling the insect vectors and removing diseased plants and contaminated seedlings. However, these methods were only partially successful in containing greening disease.<\/p>\n\n \n \n \n <\/picture>Alexandre Affonso\/Pesquisa FAPESP<\/span>\n

The results from recently introduced crop management techniques suggest that the fight against greening is not lost, but is far from over. Farmers are employing a combination of strategies: using healthy seedlings grown in screened nurseries, planting in rows running parallel to the orchard edges with higher tree density per hectare, increasing fertilization, applying insecticides more frequently, and eliminating psyllids and infected plants.<\/p>\n

Despite these efforts, citrus greening has continued to spread\u2014and not just in Brazil. The number of affected countries has jumped from 40 in 2006 to 126 today, where the disease causes orange and lemon trees to produce fruits that are fewer in number, smaller, more acidic, and drop prematurely.<\/p>\n

\u201cThis is a serious problem,\u201d says Jos\u00e9 Roberto Postali Parra, a professor of crop science at the Luiz de Queiroz School of Agriculture (ESALQ), University of S\u00e3o Paulo (USP). \u201cWe need to ramp up efforts against citrus greening, with stricter enforcement of laws requiring the removal of infected plants, even though they remain productive, albeit at reduced levels.\u201d Parra has participated in discussions with experts, and some have even suggested eliminating orange jasmine entirely.<\/p>\n

Carlos Alberto Lucato, chairman of the Brazilian Table Citrus Association and co-owner of Citr\u00edcola Lucato, a citrus fruit company based in Limeira, S\u00e3o Paulo, has also been actively involved in meetings with officials from the S\u00e3o Paulo government and other states, where he has provided input on policies to combat citrus greening. \u201cIf we fail to take stricter action, citrus yields in S\u00e3o Paulo could drop even further in the long run, and consumer prices will skyrocket,\u201d he warns.<\/p>\n

Growers in S\u00e3o Paulo are increasingly relocating to regions with lower rates of greening disease in neighboring states. Eighteen years ago, Citr\u00edcola Lucato stopped cultivating oranges in Limeira and shifted focus to its 320-hectare orchards in the Jales region, in northwestern S\u00e3o Paulo, and to its 1,000-hectare orchards in the municipalities of Madre de Deus de Minas and Piedade do Rio Grande, in southern Minas Gerais. \u201cIf greening spreads to these regions, we\u2019ll now know what measures to take, unlike 20 years ago when much of S\u00e3o Paulo wasn\u2019t prepared,\u201d Lucato says.<\/p>\n

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FUNDECITRUS<\/span>An infected plant with yellowing leaves and significant fruit dropFUNDECITRUS<\/span><\/p><\/div>\n

In April, Citrosuco, a leading orange juice exporter, announced the purchase of its 26th<\/sup> farm, also located in southern Minas Gerais. A month earlier, Cutrale, another major juice processor, revealed a R$500 million investment to establish a 5,000-hectare orchard in Sidrol\u00e2ndia, Mato Grosso do Sul.<\/p>\n

Zeroing in on the edges<\/strong>
\nDuring Expocitros, a citrus trade fair held in June in Cordeir\u00f3polis, S\u00e3o Paulo, crop scientist Franklin Behlau of FUNDECITRUS described the severity of the problem using Pera sweet orange orchards as an example. When 25% of a tree is infested, its yield drops by about 20%. If up to 50% of the tree is affected, fruit yield decreases by 40%, and in the most advanced stages, with the entire tree infected by the bacteria, the harvest can shrink by as much as 70%.<\/p>\n

In the early 2000s, in an effort to deter the loss of orange groves in the United States, research teams from the US Department of Agriculture, led by plant epidemiologist Timothy Gottwald, discovered that the rate of infestation decreases from the edges inward in citrus orchards. This finding was key in controlling the disease-spreading insects.<\/p>\n

\u201cTrees planted within 150 meters of the orchard\u2019s outer boundary host 80% of the psyllids,\u201d notes FUNDECITRUS crop scientist Renato Bassanezi. This suggested that concentrating psyllid traps and insecticide spraying along the orchard edges would be more effective. Planting rows parallel to the orchard edges has been shown to reduce the incidence of disease by 20%, while perpendicular rows facilitate the spread of insect vectors. This strategy was detailed in a May 2013 article in Plant Disease<\/em> that laid out a blueprint for controlling citrus greening.<\/p>\n

At Expocitros, Eduardo Girardi, a crop scientist with the Brazilian Agricultural Research Corporation\u2019s (EMBRAPA) Cassava and Fruit unit, proposed another potential solution to help manage greening: the use of dwarfing rootstocks (onto which fruit-bearing varieties are grafted), which reduce tree size by around 50%.<\/p>\n

\u201cThese dwarfing varieties, like others, are still susceptible to greening, but their smaller shoot size makes it easier to spray insecticides, which helps lower disease incidence,\u201d he explained. In an experiment with 500 Valencia orange trees, the flying dragon rootstock, the only dwarfing variety among the 16 tested, showed the lowest incidence rate\u201417% after eight years since planting\u2014while others saw rates as high as 48%.<\/p>\n\n \n \n \n <\/picture>Alexandre Affonso\/Pesquisa FAPESP<\/span>\n

Other strategies fell short.<\/strong> Pheromones\u2014volatile chemical compounds that spread through the air and help animals of the same species communicate\u2014worked well in lab tests to attract psyllids but failed in field conditions.<\/p>\n

In 2019, one of the insecticides used against psyllids, dimethoate, was banned following demands from European buyers of Brazilian citrus over concerns about human health risks. Later, it was discovered that psyllids had developed resistance to other insecticides, which were applied more frequently and without proper rotation. As a result, greening infestation rates rose.<\/p>\n

Researchers found an alternative: spraying with kaolin, a white powder made mainly of the mineral kaolinite. In field trials, a 2% dilution in water significantly reduced the number of psyllids landing on orange tree leaves, without apparent harm to the plants. \u201cGrowers are already using kaolin in commercial orchards,\u201d says Marcelo Miranda, a crop scientist at FUNDECITRUS.<\/p>\n

Another approach is the use of Tamarixia radiata<\/em>, a natural enemy of psyllids, which destroys the developing pests. \u201cWe discovered the wasp in 2006 in orchards in Piracicaba and Jaboticabal,\u201d says Parra (see<\/em> Pesquisa FAPESP issue n\u00b0 261<\/em><\/a>). The wasp is now being bred in two production units in S\u00e3o Paulo and should be released in abandoned orchards, isolated trees, or organic groves, where chemical pesticides cannot be used. According to Parra, combining three strategies\u2014insecticide application, biological control, and early removal of infected plants\u2014can cut disease incidence by 74%, based on a study published in May 2023 in the journal Entomologia Generalis<\/em>.<\/p>\n

In Florida, where the disease emerged in 2005 and citrus yields plummeted by over 80%, attempts to slow down greening by boosting plant nutrition have had little success. US experts are testing the effectiveness of injecting antibiotics into tree trunks to reduce greening symptoms. In areas where the disease is incipient, they focus on quickly identifying and removing infected plants. In California, they are even experimenting with dogs trained to detect the scent of infected trees before symptoms appear.<\/p>\n

\u201cWe\u2019re still fighting a war with no end in sight,\u201d Girardi remarks. To be effective, controlling insect populations needs to be a collective effort, like government measures to control the mosquitoes that spread dengue fever. However, as he notes, \u201cnot all farmers are as willing or financially capable of properly managing their orchards.\u201d Lucato witnessed this firsthand during a visit to Minas: \u201cA fellow grower told me he wanted to renew his orchard, but it was no use because his neighbor wouldn\u2019t remove the greening-infested trees from his.\u201d<\/p>\n

The story above was published with the title “The long battle against citrus greening<\/strong>” in issue 343 of September\/2024.<\/p>\n

Project
\n<\/strong>Measures for reducing primary infections through integrated management of Huanglongbing in the citrus belt of S\u00e3o Paulo: Technical and economic feasibility (n\u00ba 17\/21460-0<\/a>); Grant Mechanism<\/strong> Thematic Project; Principal Investigator <\/strong>Renato Beozzo Bassanezi (Fundecitros); Investment<\/strong> R$5,666,086.32.<\/p>\n

Scientific articles<\/strong>
\n<\/strong>BASSANEZI, R. B. et al<\/em>. Efficacy of area-wide inoculum reduction and vector control on temporal progress of huanglongbing in young sweet orange plantings<\/a>. Plant Disease<\/strong>. Vol. 97, no. 6, pp. 789\u201396. May 14, 2013.
\nGARCIA, A. G. et al<\/em>. The importance of Integrated Pest Management to flatten the huanglongbing (HLB) curve and limit its vector, the Asian citrus psyllid<\/a>. Entomologia Generalis<\/strong>. Vol. 42, pp. 349\u201359. May 18, 2022.
\nRODRIGUES, J. D. et al<\/em>. Huanglongbing incidence, canopy volume, and sprouting dynamics of \u201cValencia\u201d sweet orange grafted onto 16 rootstocks<\/a>. Tropical Plant Pathology. <\/strong>Vol. 45, pp. 611\u201319. Oct. 17, 2020.<\/p>\n","protected":false},"excerpt":{"rendered":"Greening was one of the main causes of a 25% drop in yield in the last harvest","protected":false},"author":17,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":""},"categories":[169],"tags":[1637,153,209,224,200],"coauthors":[5968],"class_list":["post-545767","post","type-post","status-publish","format-standard","hentry","category-technology","tag-agriculture","tag-agronomy","tag-biology","tag-ecology","tag-environment"],"acf":[],"_links":{"self":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/545767","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/users\/17"}],"replies":[{"embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/comments?post=545767"}],"version-history":[{"count":4,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/545767\/revisions"}],"predecessor-version":[{"id":546321,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/posts\/545767\/revisions\/546321"}],"wp:attachment":[{"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/media?parent=545767"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/categories?post=545767"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/tags?post=545767"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/revistapesquisa.fapesp.br\/en\/wp-json\/wp\/v2\/coauthors?post=545767"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}