Citrus canker in lemon orchards: symptoms, spread and what growers can do

On 29 March 2026 Jagonews24 published a practical guide by Samiran Biswas, an agriculture and environment specialist, on what growers should do when lemons and other citrus fruit, such as oranges and malta, are attacked by canker. The writer called canker one of the most harmful and serious diseases of lemon, and set out its symptoms, its causes, the orchard care that keeps it down and the copper sprays used against it. This report retells that advice for growers, checks it against published plant-pathology research and adds the background a farmer needs: what the bacterium is, how it travels from tree to tree, and what researchers in Bangladesh found when they studied it.

Canker is caused by the bacterium Xanthomonas citri subsp. citri, also written Xanthomonas citri pv. citri and often shortened to Xcc. It attacks every part of the tree above the ground, including leaves, twigs, young shoots and fruit. The European and Mediterranean Plant Protection Organization (EPPO), on information dated 2024, lists the disease as present in Bangladesh with a restricted distribution, and a 2018 review in the journal Molecular Plant Pathology lists Bangladesh among the countries where it occurs locally.

The writer noted that citrus ranks second among the world's fruits by production. An introductory chapter in the 2023 book Citrus Research, drawing on FAO statistics, gives the same rank for 2021: citrus fruit was the second most produced fruit worldwide that year, with 161.8 million tonnes harvested from more than 10.2 million hectares. Oranges made up the largest part, at 75.57 million tonnes, followed by tangerines at 41.95 million tonnes.

Citrus is grown commercially in more than 140 countries, according to a 2024 study in the journal Plant Science Today by plant pathologists of Bangladesh Agricultural University (BAU) in Mymensingh, the Bangladesh Agricultural Research Institute (BARI) and the Department of Agricultural Extension (DAE). The study says citrus does best in well-drained light loam soils with a pH between 4 and 9, an optimum soil temperature for root growth of about 25 °C and annual rainfall of 75 to 125 cm, and that in Bangladesh it is grown on a small scale in private orchards and commercial plantations. More than 18 citrus species are cultivated in the country, the authors wrote, and canker poses a major threat to most of them.

The guide named the citrus that Bangladesh's climate suits best: elachi lebu, kagzi lebu, pomelo (jambura), oranges and malta. Lemon is an everyday fruit in Bangladeshi kitchens, used to sharpen the taste of food and to make sherbet.

A month before the guide appeared, the Daily Observer, in a report carried by the trade site FreshPlaza on 27 February 2026, gave a picture of one of the country's lemon hubs. Lemons were grown on 1,235 hectares in Srimangal upazila of Moulvibazar district, with an average annual yield of 9 to 10 tonnes per hectare, and about 7,500 tonnes were expected that season. About 80 percent of the crop is picked in the main season and about 20 percent off-season. The upazila agriculture office said output matched official figures, though drought and water shortage had reduced it slightly.

In neighbouring Sylhet district the large jara lemon is grown in Jaintapur, Gowainghat, Kanaighat, Golapganj and Beanibazar upazilas, The Business Standard reported in April 2022, and BARI's citrus research centre at Jaintapur has long carried out research on the fruit.

Citrus canker was first described scientifically in the United States, where it broke out in several south-eastern states in the early 1900s. A researcher named Hasse received samples from Florida, Texas and Mississippi in 1914, isolated the bacterium and in 1915 named it Pseudomonas citri. It was later moved to the genus Xanthomonas, and after several changes of name Xanthomonas citri subsp. citri was formally validated in 2007, the Molecular Plant Pathology review records. The bacterium is a rod-shaped, Gram-negative, aerobic organism with a single polar flagellum, and it forms yellow colonies when grown on culture media.

Where the disease began is disputed. A 2023 review in the journal Plants says the oldest evidence comes from herbarium specimens kept in England: Citrus medica collected in India between 1827 and 1831 and Citrus aurantifolia collected in Indonesia between 1842 and 1844 already carry canker lesions. Other researchers suspected southern China. The review concludes that the disease most likely arose in tropical Asia, in areas such as India, Indonesia and China.

The common form is known as Asiatic canker, or canker A. Pathotype A attacks a broad range of citrus. Two related variants, A* and Aw, cause lesions under natural conditions only on Mexican or key lime and alemow, and two further forms, known as cancrosis B and C, are caused by a separate pathovar, Xanthomonas citri pv. aurantifolii. The review in Molecular Plant Pathology ranks grapefruit, lime and lemon as the most susceptible hosts, sweet orange as moderately susceptible, and kumquat and calamondin among the least susceptible.

Bangladesh's own strains have been studied. A 2013 disease note in the journal Plant Disease reported the first finding of pathotype A of sequence type 1 in lime and lemon fruit originating from Bangladesh. The 2024 BAU, BARI and DAE study collected 54 isolates of the bacterium from canker-infected leaves, twigs and fruit of BARI kagzi lebu-1, jara lemon, seedless lemon, Colombo lemon, BARI Malta-1, local lemon, batabi lebu, BARI Komola, satkora and other citrus, in areas including Sylhet, Moulvibazar, Khagrachari, Jamalpur, Tangail and Mymensingh. All were identified as Xcc of type A, the cause of Asiatic canker.

When the researchers tested the isolates on citrus leaves, 2 of the 54 (3.71 percent) were aggressive, 34 (62.96 percent) moderately aggressive and 18 (33.33 percent) weakly aggressive, with no link between aggressiveness and either the host or the place the sample came from. The isolates that caused the most severe symptoms were those on kagzi lemon. Comparing them with isolates from elsewhere, the authors suggested that the bacterium may have entered the country through the movement of planting material, and wrote that controlling canker is essential if Bangladesh is to produce export-quality citrus.

The guide explained that the bacteria usually enter the tree through wounds and through the leaf pores (stomata), so the risk of infection rises in the rainy season when strong winds wound the trees. Storms and rain bring more disease because canker is a waterborne bacterial infection, which is why it is seen most in the monsoon. Research supports that account closely.

The Molecular Plant Pathology review describes wind-driven rain as the way the bacterium is spread. The amount of bacteria is highest just after living lesions are wetted, and although rainwater carries fewer bacteria after about an hour of rain and wind, the bacteria multiply fast enough between storms to supply a fresh load for each new storm. Temperatures between 20 and 30 °C support good growth of the bacterium, so tropical and subtropical regions can hold large populations all year. Frequent, short tropical rains with strong gusty winds are highly favourable to spread; stronger winds wound more tissue and cause heavier infection, and hurricanes and tornadoes can carry the bacteria over long distances.

Once inside, the bacterium enters through wounds and through natural openings, the stomata and the hydathodes at the leaf edge. Under the best conditions of temperature, humidity and inoculum, symptoms can appear about seven days after infection; when temperatures or bacterial numbers are low, they can take two months or more. Young, expanding leaves, shoots and fruit are the most at risk, and tissue becomes more resistant as it matures. Stems infected while still green, however, can keep the bacteria alive for years and release them from their raised, corky lesions whenever they are wetted.

The guide said the germ can survive in the soil for 8 to 10 days and is quickly destroyed by light or sunshine. The research describes survival differently: the bacterium lives mainly within the lesions on the tree. Outside lesions it survives only one to three days on surfaces such as clothing and farm tools, and no more than two months in soil, where it loses out to other microbes. In practice this means the main store of the disease is the infected leaves, twigs and fruit on and under the trees, which is why the guide's advice to collect and burn them matters.

People and planting material carry the disease further. The review notes that infected nursery trees, once planted in the field, become sources of bacteria that rain and wind carry to the surrounding trees, and the 2023 review in Plants advises cleaning tools and workers and using tools carefully so as not to wound trees, in orchards and nurseries alike.

According to the guide, canker affects the branches, fruit, leaves, fruit stalks and shoot tips. At first small yellow spots appear on the affected parts; later they merge and become thick and large. These blister-like spots have a yellow halo around them, seen mostly on the leaves. The disease leaves raised brown blister spots on leaves, fruit and stems, on both the upper and lower sides of the leaf, and spots that start yellow gradually turn brown. Infected leaves fall, the upper leaves of the tree drop, new leaves grow poorly and become deformed, the fruit skin sometimes cracks, and a severe attack can kill the tree.

The research literature gives the same picture in more detail. On leaves, the review in Plants says, the first signs are raised round spots of 2 to 10 mm, usually first on the underside, and lesions then appear on both sides of the leaf. They start as soft, blister-like eruptions, white or yellow, then harden, turn light tan and become rough, corky canker lesions, often with a water-soaked margin. The centre of a leaf lesion later sinks and can fall out, leaving a shot-hole effect. Early leaf fall and the gradual dying back of twigs are the main problems for the tree as the disease worsens.

On twigs and fruit the lesions are raised, with an oily or water-soaked margin; twig lesions usually have no yellow halo, while fruit lesions may. Fruit lesions often have a sunken centre but do not go deep into the peel and do not affect the inside of the fruit. Even so, early fruit drop and blemished fruit are the disease's main economic effects, because cankered fruit is rejected by the fresh-fruit trade.

The guide named the citrus leaf miner, a small insect whose larvae tunnel inside leaves, as a cause that brings on canker, and advised growers to inspect lemon fields regularly and act as soon as an attack appears. The research agrees that the insect makes canker much worse, although it does not carry the bacterium itself.

The Asian citrus leafminer, Phyllocnistis citrella, is a moth. Mated females lay eggs on expanding leaves, and the larvae tunnel under the leaf's outer skin to feed. The Molecular Plant Pathology review explains that these tunnels act as wounds that expose the inner leaf tissue to infection; canker lesions that form where leafminers have fed are larger, denser and produce more bacteria than infections through the stomata. The insect feeds and breeds rapidly on the vigorous flushes of young citrus trees, which is one reason canker is more severe in young orchards. All types of citrus are attacked, but grapefruit, tangerine and pummelo are its preferred hosts.

According to the review, the larvae are controlled mainly with insecticides of the abamectin and neonicotinoid groups in the countries where the research was done. Biological control has limited success: the best-known natural enemy, a small wasp called Ageniaspis citricola, can parasitise many larvae, but it has not proved as effective as chemical sprays when infestations are heavy. Growers in Bangladesh should ask the upazila agriculture officer which leafminer treatment is registered and recommended locally, and at what dose and timing.

The guide's first line of defence is good orchard management, which it called organic management. Its steps were:

• When setting up an orchard, keep the correct spacing between seedlings; if necessary, leave a little more room between plants and between rows so that stormy winds do not wound the trees.
• Collect disease-free lemon seedlings from healthy, vigorous mother trees and plant only those.
• Inspect the lemon field regularly for leaf miners and take control measures as soon as an attack appears.
• Collect diseased leaves, branches and fruit and burn them.
• Work in the orchard while the leaves are dry.
• Prune lemon trees before the monsoon and burn the prunings, then apply Bordeaux mixture at the correct dose.
• Uproot dead trees killed by canker and burn them quickly.

These steps match what the research recommends. The 2023 review in Plants says that pruning or stripping infected summer and autumn shoots before a monsoon and burning them helps control the spread of canker, and that copper sprays combined with pruning have proved useful against small outbreaks. It also lists regular inspection of orchards, so that the disease is found early, and cleaning tools and workers.

Where canker is established, the Molecular Plant Pathology review describes an integrated programme: planting canker-free nursery stock, choosing less susceptible cultivars, planting windbreaks of trees, spraying copper-based bactericides, controlling the leafminer and using products that switch on the tree's own defences. Clean planting material matters because infected nursery trees become sources of bacteria in a new orchard, and because young trees, which put out new leaves more often, are more susceptible. Delaying the arrival of the disease in a new orchard can therefore significantly reduce its impact.

Windbreaks deserve particular mention in a country of monsoon storms. A barrier of trees reduces the force of the wind on the orchard, which lowers both the spread of the bacteria and the number of wounds through which they enter. Windbreaks combined with copper sprays are described in the review as highly effective, and in Argentina, levels of canker on trees protected by windbreaks were lower than on trees treated with copper sprays.

For chemical control, the guide recommended copper oxychloride or another copper product, sprayed when the first symptoms appear and repeated through the rainy season, since storms and rain bring more disease; it said the spray can also be used as a preventive, and that Bordeaux mixture should be applied after pruning.

Copper is indeed the standard chemical tool against canker, but the research is clear about its limits. The Molecular Plant Pathology review says copper sprays are strictly preventive, with no curative or systemic action: copper reduces the build-up of bacteria on new leaf flush and protects the surfaces of expanding fruit and leaves from infection, but it does not cure lesions that already exist. Fixed or insoluble forms such as copper hydroxide, copper oxychloride and copper oxide are the most widely used. They leave an insoluble copper film on the treated surface that kills bacteria arriving on it, and because they release copper slowly they are less harmful to the plant and last longer than soluble forms.

The amount of copper and how often it is sprayed depend on the weather and on how long protection is needed, the review says. Copper is usually applied in the seasons when young tissue is plentiful and the weather favours the bacterium. The protective film thins as leaves and fruit grow, so repeat sprays are needed, and fruit that keeps expanding over 90 to 120 days, depending on the cultivar, needs repeated cover even behind windbreaks. Copper alone is not enough on susceptible citrus in stormy weather, because wind-blown rain drives the bacteria straight into the stomata, past the copper film, which is why the review calls the combination of copper sprays and windbreaks essential when conditions favour outbreaks.

Copper also has costs. Sprayed copper builds up in the soil, where it can harm root growth and the tree's uptake of nutrients; high concentrations can blemish the fruit; and frequent use encourages copper-resistant strains of the bacterium, which could make future control harder. That is the reason behind the guide's own warning not to overuse the chemical.

The guide also gave a dose and a spraying schedule for copper oxychloride. This report does not repeat them, because they could not be matched to a published recommendation of the Department of Agricultural Extension (DAE), the Agriculture Information Service (AIS) or BARI, and the strength of copper products differs from brand to brand. Before spraying copper oxychloride or Bordeaux mixture, growers should use a product registered in Bangladesh, follow its label, and ask the upazila agriculture officer or the local sub-assistant agriculture officer for the dose and the interval between sprays.

The guide ended with precautions for anyone spraying:

• Spray in the morning or late afternoon, when the sun is weaker.
• Do not use more than needed.
• If rain washes off the spray, spray again.
• Wear gloves and a mask while spraying.
• Wash hands and face thoroughly after spraying.
• Stop spraying some days before harvest; the waiting period for each product is given on its label.
• Store the chemical in a dry, cool place out of the reach of children.

Canker does great harm to the citrus trade. Because blemished fruit is rejected by fresh-fruit buyers, and because the bacterium is treated as a quarantine organism by citrus-producing countries that are free of it or have eradicated it, the disease shuts markets. The Molecular Plant Pathology review records that it has been eradicated from South Africa, Australia and New Zealand and is absent from Europe.

Eradication is costly. The 2023 review in Plants describes Florida's Citrus Canker Eradication Program, which from the end of 1999 applied a rule that every citrus tree within 1,900 feet (579 m) of an infected tree was removed, chipped and buried, with replanting allowed only after an area had been free of canker for at least two years. The rule met strong opposition from growers and was suspended in January 2006 as economically unsustainable, and eradication programmes were ended in Florida in 2006 and in Brazil in 2009. Where the disease is established, growers rely instead on the integrated management described above.

For Bangladesh the cost has been in exports. The 2024 BAU, BARI and DAE study, citing the DAE's Plant Protection Wing, said the country exports jara lemons grown in greater Sylhet and Colombo lemons grown mainly in Narsingdi, earning 75 crore taka in the fiscal year then under way, but that canker has reduced citrus exports by about 50 percent, and that at one point the export of jara lemons to Europe was halted. The Business Standard reported in April 2022 that citrus exports from Sylhet to Europe and America had been stopped for about 15 years, after the United Kingdom banned the imports in 2007 because of canker.

Photo: David Bartels, USDA APHIS / Wikimedia Commons (public domain)

Sources: Jagonews24, Molecular Plant Pathology (Ference and others, 2018), Plants (2023 review of citrus canker), Plant Science Today (Bangladesh Agricultural University, BARI and DAE, 2024), Plant Disease (Vernière and others, 2013), European and Mediterranean Plant Protection Organization (EPPO) Global Database, Citrus Research (IntechOpen, 2023, FAO data), Daily Observer via FreshPlaza (27 February 2026), The Business Standard (April 2022)