First detected in Asia more than 100 years ago, greening is a disease that was identified in Brazil in 2004. Today, it is present in all citrus regions of São Paulo and in the orchards of Minas Gerais, Goiás, Mato Grosso do Sul, Santa Catarina and Paraná, causing great concern.
Known as one of the most dangerous diseases in citrus plantations, greening or Huanglongbing (HLB) affects production, reduces fruit quality and shortens the life of orchards.
Given the dangerous nature of citrus greening, we invited Alécio Souza Moreira, agronomist and analyst at Embrapa Cassava and Fruit Farming, to talk about this disease and strategies to protect production.
What is greening and how does it manifest itself in plants?
Known as the yellow branch disease, greening, better known as HLB, is one of the most dangerous diseases on citrus plantations worldwide.
Caused by the bacterium Candidatus Liberibacter asiaticus, plants infected by the bacterium have yellowish leaves with asymmetrical spots, in addition to thick and yellowish ribs.
Infected fruits, on the other hand, have irregular ripening with deformations, in addition to smaller size and asymmetry in the columella. The disease also causes them to fall prematurely, which affects the production of infected plants.
Since there is still no cure for the disease, the best way to deal with greening is prevention.
Impact on citrus production potential
According to the Embrapa researcher, the main impacts on citrus production are related to the eradication of plants showing symptoms of the disease and the early drop of fruit.
“Such problems end up affecting the production potential of a citrus plant,” says Alécio Moreira.
In order to get a better view, data from the Citrus Defense Fund’s Crop Estimation Program (Fundecitrus) indicate that greening is responsible for about 8% of the decline in sweet orange fruit in the citrus belt.
Another estimate from Fundecitrus indicates that in the 2024-25 cycle it could cause a 24% drop in production due to several factors, including the high incidence of greening and other diseases and pests.
If the forecast is confirmed, it will be the lowest citrus production result in the last ten harvests, according to the Fundecitrus analysis.
Propagation of greening
The species Candidatus Liberibacter asiaticus (predominant in Brazil) and Ca. Liberibacter americanus can be spread by grafting methods and mainly by the psyllid Diaphorina citri.
“If it feeds on a plant with the bacterium, it can acquire it and transmit it by feeding on a healthy plant,” adds Moreira.
The big problem is when symptoms appear on the leaves or fruits at the end of the branches. This is an indication that the bacterium has already spread throughout the plant, including the lower part of the trunk and roots.
Therefore, pruning branches with symptoms is useless and even dangerous. In addition to not curing the plant, the shoots that arise grow pruning are an attraction for the vector insect, which will acquire the bacteria and spread it to healthy plants, causing new infections.
Continuous monitoring is essential!
For the Embrapa researcher, proper management to contain greening begins with efficient monitoring of the citrus psyllid, the vector of the disease, and also of HLB.
“A good monitoring of the disease and the vector is important to know which are the critical regions where the disease occurs and which are the most threatened harmless regions”.
Normally, Moreira explains that this monitoring occurs through visual inspections, at least quarterly, of all plants by people trained and experienced in this activity.
“The objective is the visual detection of the typical symptoms of the disease and, if necessary, confirmation by molecular analysis in a laboratory of the plant tissue sampled.”
The vector psyllid is monitored every two weeks by means of yellow adhesive cards placed in the upper third of the citrus plants at the edges of the citrus orchards.
The reading of these cards to identify the psyllids should also be done by a trained person in a quiet and suitable place.
Based on the monitoring information, Moreira explains that it is possible to draw up strict strategies for managing the disease and the vector to avoid an increase in the incidence of the disease.
It is also important to develop prevention strategies for areas where the disease has not yet been reported in order to prevent its entry.
Immediate action remains important
In addition to continuous monitoring, some immediate actions are also necessary. If greening is detected on a plant, it must be immediately eradicated from the orchard.
However, before cutting and uprooting the infected plant, it is recommended that it be sprayed with an insecticide. “This measure prevents the spread of any psyllids that may be present in the plant,” explains the researcher.
After cutting, the remaining wood should be treated with herbicide to prevent the plant from growing new shoots.
After the period of residual herbicide action, a new seedling can be planted in the place where the plant was eradicated (replanting).
Healthy Citrus Recommendations
Check out some tips to keep crops healthy, productive and free of greening:
- Select an appropriate planting site;
- Plant quality seedlings (health, genetics and vigor);
- Reduce the period of exposure to psyllids;
- Consider spraying insecticides with the edge band at intervals of 7 to 14 days, depending on the incidence of the insect;
- Inspect and eradicate infected plants to prevent outbreaks of disease transmission;
- Monitor and control the presence of the psyllid
In recent years, Moreira explains, research has been conducted to automate vector surveillance through artificial intelligence systems.
“There is still no tool in this sense being commercialized on a large scale, but it is a very interesting possibility,” he says.
Drones have been used in insecticide spraying in areas that are more difficult to access and also in the release of Tamarixia radiata, a wasp that acts as a biological control of the vector.
Since there is no cure, the best way to combat greening is to prevent its occurrence by taking preventive measures, such as choosing a suitable planting site, using healthy seedlings, and frequently monitoring the planting area.
Just do it and get rid of this disease!
