Common Citrus Pests and Diseases: Identification and Control

Citrus crops – oranges, lemons, mandarins, limes, and grapefruit – are among the most economically important fruit crops worldwide. Yet, year after year, growers face a persistent challenge: insect pests and diseases that silently eat into yields, downgrade fruit quality, and in severe cases, kill entire trees. According to CABI’s BioProtection Portal, citrus crops are threatened by a wide range of insects, mites, fungi, bacteria, and viruses – all capable of causing severe economic loss. Early identification and a well-planned management strategy are what separate a productive orchard from a failing one.

Major insect pests of citrus 🔗

Several key insects target citrus trees at various growth stages. Knowing what to look for is the first step toward effective control.

Citrus psylla (Asian citrus psyllid) 🔗

The Asian citrus psyllid (Diaphorina citri) is arguably the most dangerous insect pest of citrus globally. It is a tiny, mottled brown insect (3-4 mm) that feeds and lays eggs on young shoots. While the feeding itself causes leaf curl and distortion, the real threat is indirect: the psyllid is the primary vector of Huanglongbing (HLB), or citrus greening disease, caused by the bacterium Candidatus Liberibacter asiaticus. Once a tree is infected with HLB, it cannot be cured.

The adult psyllid has a distinctive feeding posture – head angled downward with the rear end raised at about 45 degrees – unlike any other citrus insect pest. Females lay tiny yellow-orange eggs on freshly emerging leaf flushes, and nymphs develop exclusively on young growth. Management requires multiple insecticide applications, as no single product fully controls all life stages. Contact insecticides are often limited in effectiveness because eggs and nymphs are tucked inside new foliage while adults are highly mobile. Systemic insecticides, windbreaks of at least 12 feet, and mesh barriers around orchards all form part of an integrated approach.

Citrus leaf miner 🔗

The citrus leafminer (Phyllocnistis citrella) is a small moth native to Asia whose larvae cause characteristic damage to young citrus foliage. Larvae create shallow, meandering tunnels – referred to as mines – just under the surface of young leaves, causing them to curl and look distorted. The damage is easy to identify: silvery, serpentine trails winding across new growth, often with a thin dark frass line running through the middle.

Mature citrus trees (more than 4 years old) generally tolerate leafminer damage without significant impact on fruit yield. However, young nursery trees and new plantings are far more vulnerable, as infestations can noticeably retard growth. The leafminer has also been linked to increased susceptibility to citrus canker, since the mining wounds provide entry points for the bacterial pathogen. For established trees, allowing natural enemies such as tiny parasitic wasps to parasitize the larvae is often more effective than chemical intervention – broad-spectrum sprays tend to kill these beneficial insects and trigger secondary outbreaks of mites and scale. For young trees, soil-applied systemic insecticides like imidacloprid or cyantraniliprole, applied after bloom, offer good protection.

Whiteflies 🔗

Citrus whiteflies are small, sap-sucking insects whose nymphs and adults feed on the underside of leaves. The citrus whitefly nymph is small, flat, and feeds on the lower leaf surface, as does the adult. Heavy infestations weaken trees by draining sap and, importantly, by producing honeydew – a sticky secretion that promotes the growth of sooty mould fungus. This sooty mould coats leaves and fruit surfaces, reducing photosynthesis and significantly downgrading the marketable quality of fruit. Management involves avoiding over-application of broad-spectrum pesticides (which destroy natural predators), using selective insecticides, and encouraging biological control agents like parasitic wasps of the genus Encarsia.

Citrus mites 🔗

Citrus rust mites and spider mites are microscopic pests that cause surface damage to fruit and foliage. Citrus rust mites have an elongated, wedge-shaped body and are approximately 0.13 mm long – difficult to see with the naked eye. Fruit attacked by rust mites develops a characteristic tarnished brown or bronze appearance on the rind, though the internal fruit quality is not affected. Mite populations are typically highest during summer months. Horticultural mineral oils are effective treatments, and high-pressure water sprays can also dislodge spider mites from foliage. Care must be taken when selecting chemical controls, as certain insecticides – particularly imidacloprid – can trigger mite population explosions by eliminating predatory insects.

Bark-eating caterpillars 🔗

Bark-eating caterpillars (Indarbela spp.) are a damaging pest in many Asian citrus orchards. The larvae bore into the bark and wood of branches and trunks, feeding on the inner tissue and creating irregular patches of chewed bark covered with silk webbing and frass. This girdling disrupts the transport of water and nutrients within the tree, causing dieback of affected branches and, in severe cases, the death of the entire tree. Management involves physically removing the webbing and frass, inserting a petrol-soaked swab or injecting insecticide (such as chlorpyrifos) into the borehole, and then sealing it with mud. Affected bark should be scraped clean and treated with a copper-based paste to prevent secondary infection.

Major diseases of citrus 🔗

Citrus diseases are caused by a range of pathogens – bacteria, fungi, viruses, and nematodes – each requiring a different management approach.

Citrus canker 🔗

Citrus canker is one of the most widespread and economically devastating bacterial diseases of citrus worldwide. It is caused by the bacterium Xanthomonas axonopodis pv. citri and affects all aerial parts of the plant – leaves, fruits, twigs, thorns, and bark – producing hard, corky cankers that are easily identified on infected plants. Young lesions first appear as raised spots on both leaf surfaces, later becoming crater-like with a raised margin surrounded by a yellow halo. On fruit, the lesions reduce marketability severely even though the fruit itself remains safe to eat.

Wind-driven rain is the primary dispersal agent, and the pathogen spreads readily during the monsoon season. IPM practices include pruning badly infected twigs before the onset of monsoon, establishing windbreaks around orchard borders to slow pathogen spread, and controlling leafminers on young flush – since leafminer wounds serve as entry points for the bacterium. Chemical management involves fortnightly sprays of streptomycin sulphate (500-1,000 ppm), phytomycin (2,500 ppm), or copper oxychloride (0.2%).

Citrus scab 🔗

Citrus scab is a fungal disease caused by Elsinoë fawcettii. It produces wart-like, corky lesions on leaves, twigs, and fruit surfaces. The lesions are raised and rough to the touch, and on fruit they cause significant deformity that reduces commercial value. The disease thrives under cool, humid conditions and spreads via airborne spores during wet weather. Management involves applying approved copper-based or other registered fungicides during periods of flush growth and wet weather, removing and destroying infected plant material, and using resistant rootstocks where available.

Gummosis 🔗

Gummosis is one of the most visually recognisable diseases of citrus. It is caused by several Phytophthora species – including P. parasitica, P. palmivora, and P. citrophthora – and is primarily manifested as extensive bark rotting and gum exudation at the base of the trunk. Bleeding from small cracks in bark on the lower trunk is typically the first external symptom; the oozing bark later dries, cracks, and sloughs off, with lesions slowly girdling the tree.

The pathogen’s oospores survive in soil and are splashed onto the lower trunk during rain. The disease develops rapidly under moist, cool conditions, but hot summer weather slows its spread and aids healing of lesions. Cultural management includes selecting well-drained planting sites, avoiding wounding of the crown root area during orchard operations, planting on raised mounds with the graft union above soil level, and using Phytophthora-tolerant rootstocks such as trifoliate orange or swingle citrumelo. Where lesions are detected early, removing the diseased bark with a clean knife down to healthy tissue and applying a Bordeaux mixture (copper sulphate + lime + water, 1:1:10) is an effective chemical treatment. Systemic fungicides can also provide control when applied promptly.

Citrus tristeza virus 🔗

Citrus tristeza is a devastating virus disease caused by Citrus tristeza virus (CTV). Symptoms appear on all parts of the plant – leaves develop a yellow mosaic pattern, and inner stem portions show characteristic pitting – and in severe cases, the entire tree can dry up and die, resulting in up to 100% loss from an infected tree. The virus is transmitted primarily by the brown citrus aphid (Toxoptera citricida) and persists in infected plant tissue.

Since no effective chemicals exist against viruses, management is entirely preventive. Avoiding susceptible rootstocks – particularly for sweet orange and mandarin cultivation – is the most critical cultural measure. Pre-immunisation of nursery seedlings with mild, cross-protective strains of CTV has proven effective in commercial orchards: a mild strain inoculated into the plant suppresses the impact of a subsequent challenge by a virulent strain. Certified disease-free budwood and aphid vector control through insecticide sprays also form core components of tristeza management.

Citrus greening (Huanglongbing) 🔗

Citrus greening, caused by the bacterium Candidatus Liberibacter asiaticus, is widely considered the most destructive citrus disease in the world today. Infected trees show yellowing of leaves on specific branches, while fruit remains partially green even at maturity and develops a bitter taste – making it completely unmarketable. The disease is transmitted by the Asian citrus psyllid and through the use of infected budwood in grafting.

There is currently no cure for HLB-infected trees. Management relies on using pathogen-free budwood for propagation, aggressive psyllid vector control through insecticides, and fortnightly sprays of tetracycline at 500 ppm, which can have some suppressive effect on the bacterium in infected plants. Infected trees should be removed and destroyed promptly to prevent the disease from spreading to healthy trees in the orchard.

Citrus nematodes 🔗

Citrus nematodes – primarily the citrus nematode (Tylenchulus semipenetrans) causing slow decline, and the burrowing nematode (Radopholus similis) causing spreading decline – attack the root system of citrus trees. Infected trees show gradual yellowing, reduced vigour, smaller leaves, poor fruit set, and, in advanced cases, complete collapse of the root system. Nematode populations are difficult to detect without soil sampling and laboratory analysis. Management includes using nematode-resistant or tolerant rootstocks (such as trifoliate orange), soil fumigation before planting in heavily infested fields, post-planting application of nematicides, and maintaining good soil organic matter to encourage beneficial soil microorganisms that suppress nematode populations.

Integrated pest management (IPM) for citrus orchards 🔗

Effective management of citrus pests and diseases requires accurate identification combined with IPM strategies – the ecologically-based approach that allows for chemical pesticide use only when genuinely needed. A well-designed IPM programme for citrus combines three pillars: cultural, biological, and chemical control.

Cultural controls 🔗

Cultural practices form the foundation of any IPM plan. These include using certified disease-free planting material and resistant rootstocks, pruning infected branches before the monsoon season, establishing windbreaks to slow the airborne spread of bacterial pathogens, maintaining proper orchard drainage to discourage Phytophthora, adopting drip irrigation to keep water away from tree trunks, and scheduling fertilisation and irrigation to limit excessive flush growth during peak pest activity periods. Regular and timely scouting keeps maintenance input to a minimum and enables growers to catch infestations before they escalate.

Biological controls 🔗

Biological control agents are a valuable and under-utilised resource in citrus orchards. Macrobials – such as the ladybird beetle Cryptolaemus montrouzieri – feed on soft scale insects, helping control their numbers naturally. Parasitic wasps such as Ageniaspis citricola and Cirrospilus quadristriatus are highly effective against citrus leafminer larvae. Predatory lacewings consume aphids and soft-bodied pests. Maintaining flowering plants within or around the orchard – such as dill, fennel, or coriander – provides nectar and pollen sources for adult parasitic wasps, encouraging their presence and reproduction in the orchard environment.

Chemical controls 🔗

When pest or disease pressure exceeds economic thresholds, chemical intervention becomes necessary. Selecting lower-risk pesticides that are compatible within an IPM strategy minimises harmful effects on human health and the environment. Key chemical tools include copper-based bactericides and fungicides for canker and gummosis, systemic fungicides for Phytophthora, selective insecticides for psyllid and mite control, and horticultural mineral oils (HMOs) for leafminer, scale, and mite management. IPM-based approaches can reduce pesticide use in citrus orchards by up to 50% while maintaining fruit health – making this approach both economically and environmentally advantageous. Rotating chemical groups is important to prevent resistance development, and all applications should strictly follow label directions.

What do you think? Given that diseases like HLB and tristeza have no chemical cure once a tree is infected, how can small-scale citrus growers be better supported in adopting preventive IPM practices before disease pressure builds? And with psyllid-transmitted greening now spreading into new growing regions, should resistant rootstock development and certified nursery material programmes be made a higher policy priority in citrus-producing countries?

References

1. https://bioprotectionportal.com/resources/managing-citrus-pests/
2. https://farmonaut.com/blogs/pesticide-for-citrus-trees-7-powerful-ways-to-control-pests
3. https://ipm.ucanr.edu/agriculture/citrus/asian-citrus-psyllid/
4. https://ipm.ucanr.edu/agriculture/citrus/citrus-leafminer/
5. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74137.html
6. https://hgic.clemson.edu/factsheet/citrus-insects-related-pests/
7. https://www.aces.edu/blog/topics/crop-production/citrus-pest-identification-and-management-guide/
8. https://openbooks.col.org/integrateddiseasemanagement/chapter_4-citrus-diseases-and-their-management.html
9. https://ipm.ucanr.edu/PMG/GARDEN/FRUIT/DISEASE/phytogumm.html
10. https://ipm.ucanr.edu/agriculture/citrus/phytophthora-gummosis/