HLB Citrus Disease Causes, Treatment, and Sustainable Management for Citrus Growers

Huanglongbing hlb disease in citrus or hlb citrus disease​ greening is one of the most severe citrus diseases – also known as huanglongbing citrus disease. It enters the tree vascular system thus disrupting water and nutrient transport around the tree. Older trees are less productive, lack canopy growth and miss-shaped fruit. If sian citrus psyllid symptoms do occur, there may be high level disease spread within the tree (particularly where symptoms are seen) identification and integrated management is important.

Major citrus-producing states in China (including citrus-producing areas such as Hainan), as well as citrus-producing Brazil and Mexico and the United States, could suffer significant economic losses from the disease. In the absence of a cure, the need for early monitoring of disease outbreaks, spray programs for vectors and orchard practices are emphasised to minimise spread and reduced orchard productivity is recognised as essential.

Why or How is Huanglongbing (HLB) disease in citrus?

When trees lack good health, they become weaker and symptoms like leaf or fruit malformations, dieback and whole tree decline manifest. The bacteria are systemic and once diseased, it is very difficult to effectively manage the disease. This will help ensure that they make it to some degree of successful asian citrus psyllid prevention or early hlb citrus treatment, instead of coming into production from over huanglongbing diseased trees.

What is the mode of transmission of HLB to impacted trees from Asian Citrus Psyllid?

It is when the insect feeds on an infected citrus tree that it is infected by the huanglongbing bacteria. During its life it is a carrier of infected pathogens and at the time of feeding it is an infection source for healthy trees. Asian citrus psyllid diaphorina citri vector of citrus huanglongbing disease​, is one of the most-significant associations for growers to consider when developing disease management programs since it is the vector for citrus huanglongbing (HLB).

Controlling psyllid populations when citrus is in new growth periods is important for it to reduce the spread of the disease.Both leaf-feeding adults and nymphs feed on citrus flushes; therefore, management of psyllids during these growth periods is a key factor in seedling declaration.

Early signs of Asian Citrus Psyllid and HLB?

Early recognition can permit growers to take action before the spread of infection. Common symptoms associated with common ASdi are curling of young leaves, secretion of wax covering the leaves by the nymphs, stunted flush growth and tiny dark brown insects on new shoots. Feeding injury can cause areas where bacteria can be spread.

HLB infected trees may subsequently exhibit deficits in nutrient availability, twig dieback, stunted canopies, mottling, irregular and asymmetric leaf yellows, small lopsided fruit, aborted seeds and inconsistent fruit color. These symptoms are also suggestive of nutritional disorders and so a laboratory diagnosis is sometimes suggested for precise diagnosis. 

Scouting during growing season is still one of the best management practices.

Why is HLB So Hard to Control?

Below are multiple factors that contribute to HLB as being a very difficult hlb citrus disease​.

When infected, the huanglongbing bacteria are not readily visible in the phloem making control more difficult. Sometimes there are no signs for months after infection and disease can be carried in orchards without signs. The psyllids are found on trees and multiply rapidly, and spread quickly to other trees that are susceptible, effectively endlessly spreading new infections.

Several producers have used multiple sprays of insecticides for control of psyllids. However, complete dependence on chemical control may result in increased production costs arising from the need to control desirable insects with chemicals, as well as insecticide resistance.

In the long term, when measures taken for the disease management plan are integrated (focusing on vector monitoring, biological disease control measures, orchard sanitation and prudent asian citrus psyllid pesticide application), it is more sustainable.

Treatment of citrus greening disease: What management choices do you have?

At present, no single hlb citrus treatment exists to get rid of the bacteria on an infected tree. Management programs are intended to delay dissemination of disease, limit vectors and keep trees productive as long as possible instead.

There are five factors to ensure a comprehensive strategy for citrus greening disease treatment​ ; these are regular orchard scouting, removal of severely infected trees, balanced nutrition, control of asian citrus psyllid huanglongbing, and the use of certified disease-free nursery stock.

Studies are ongoing on methods such as using antimicrobial compounds, heat therapy, nutrition and biological control organisms. The different approaches have been examined but no seemingly developed bactericide for control of citrus huanglongbing and its preparation method has been effective in citrus huanglongbing control in the field. Finally, asian citrus psyllid prevention is the basis for good orchard operation.

New approaches to control Asian Citrus Psyllid are important because of biological control

Biological control has become more widely used by growers as sustainable agriculture is a growing emphasis of use in integrated pest management (IPM) programs.

An entomopathogenic fungus, Isaria fumosorosea, is a candidate biological agent that is naturally present to infect a variety of insect pests including sap-feeding insects. Once the fungal spore lies on an susceptible insect it germinates, burrows through the insect's cuticle, reproduces in the insect and kills the insect.

Biological fungi work on several physiological targets where they replicate in their natural propagation processes and also support beneficial insect populations and can minimize chemical residues.

Zimmermann (2008) made a good review on the biology and ecological value of Isaria fumosorosea, its biocontrol of several important insect pests and its use in biological pest management programmes.

Having these properties, biological control methods are gaining increasing importance for asian citrus psyllid organic treatment and sustainable cultivation in orchards.

Novobac Fumokar supports sustainable Asian Citrus Psyllid Management

Novobac's expertise is in biological crop protection, microbial technologies and sustainable agricultural solutions to manage insect problems while promoting environmentally friendly crop production.

Novobac Fumokar is a biological insecticide containing Isaria fumosorosea for bio-management of sap-feeding insect pests including the Asian citrus psyllid. Spores stick to the insect's body after application, germinate in favourable conditions, burrow through the cuticle, and kill the pests biologically.

Fumokar will help reduce psyllid population levels and will boost Integrated Pest Management programmes by reducing HLB transmission. Biological products such as Fumokar have been used in sustainable orchard management practices as an agro-cultural and/or conventional control along with citrus growers in Canada, United States, Mexico, Brazil, Europe, India and Southeast Asia.

Long-Term HLB Management Program

There is no single solution to HLB and it can be successfully managed by an integrated, long term approach.

The successful programs include regular psyllid monitoring, early detection of disease, prompt removal of infected trees, the use of certified planting material, balanced nutrition, orchard sanitation and biological control of vectors. A measure that is most effective to prevent the huanglongbing disease spreading at the rapid rate is to keep Asian citrus psyllid populations under control before the hlb citrus disease​ is able to spread broadly.

The research developments will lead to better biological crop protection technologies; when combined with good agronomy, growers will have a more sustainable way to manage citrus orchards more efficiently and have fewer resorting to continued chemical insecticide applications.

Reference: 

•  Ullah, Muhammad Irfan, et al. "Use of the entomopathogenic fungi Beauveria bassiana (Hyphomycetes: Moniliales) and Isaria fumosorosea (Hypocreales: Cordycipitaceae) to control Diaphorina citri Kuwayama (Hemiptera: Liviidae) under laboratory and semi-field conditions." Egyptian Journal of Biological Pest Control 28.1 (2018): 75.
• Chow, Andrew, et al. "Field efficacy of autodissemination and foliar sprays of an entomopathogenic fungus, Isaria fumosorosea (Hypocreales: Cordycipitaceae), for control of Asian citrus psyllid, Diaphorina citri (Hemiptera: Liviidae), on residential citrus." Journal of Economic Entomology 111.5 (2018): 2089-2100.