Citrus Greening: A Threat to Citrus Production and How to Combat It

Case Studies

Citrus greening, also known as Huanglongbing (HLB), is a bacterial infection that poses a severe threat to citrus species worldwide. It is often a death sentence for infected trees, leading to significant yield losses and economic damage. First identified in China in the early 1900s, the disease has rapidly spread to major citrus-producing countries, including Brazil and the United States, where it has had a devastating impact on the industry, affecting growers, producers, and consumers alike. Although various strategies exist to control the spread of the disease, the question remains: How can innovative technologies like Proofminder help?

Overview of Citrus Greening Disease

Citrus greening was first documented in 1919 in Guangdong Province, South China. The disease is caused by three species of the bacterium Candidatus Liberibacter: Ca. L. asiaticus, Ca. L. africanus, and Ca. L. americanus, with the Asian form being the most widespread and destructive.

The pathogen is transmitted by the Asian citrus psyllid (Diaphorina citri), a small flying insect. The bacteria reside in the phloem, the nutrient-conducting tissue of the tree, and are spread when the psyllid feeds on the infected phloem. Once the psyllid becomes a carrier of Ca. L. asiaticus, it can infect other trees, leading to a rapid and widespread transmission of the disease.

Symptoms and Effects on Citrus Trees

Citrus greening primarily attacks the phloem of the tree, disrupting nutrient transport. Symptoms include premature fruit drop, misshapen and bitter fruit, stunted growth, and sparse canopies. Over time, infected trees become unproductive and may die within a few years, severely impacting citrus yields.

Strategies for Controlling Citrus Greening

Given the severity of citrus greening, various strategies have been developed to control its spread, although finding long-term solutions has been challenging due to the elusive nature of the bacterium. Scientists have struggled to grow the bacteria in laboratory conditions, making research and development more difficult.

Protecting Against the Bacteria and the Psyllids

Orange farmers utilize a mixture of strategies to minimize the damage caused by citrus greening.

Chemical Control: Chemical pesticides can help control psyllid populations, but insects often develop resistance, and there are environmental concerns associated with their use. Alternatively, biological control methods, such as using the wasp Tamarixia radiata, have shown promise. The wasp lays its eggs inside psyllid larvae, killing them as the wasp larvae develop. Additionally, RNA interference techniques are being explored, involving the use of viruses to introduce HLB-killing molecules into the trees.
Bacterial Protection: Farmers have attempted to combat the issue with antibiotics, but the pathogen often resides deep in the roots, beyond the reach of these treatments, raising concerns about human health risks. Plant breeding has also seen some success, such as with the HLB-tolerant variety “Super Belle,” which was developed by chance. However, creating an HLB-resistant variety remains a priority. Due to the slow pace of traditional plant breeding, researchers are turning to gene editing and other advanced biotechnological techniques.

Prevention and Early Detection

Prevention is a critical part of battling citrus greening. In China and Brazil, successful prevention strategies involve detecting and removing infected trees and monitoring and controlling psyllid populations.

How Proofminder Can help producers Mitigate the effects of Citrus Greening

Use Case 1: Dropped Fruit Counting

Premature fruit drop is one of the most critical symptoms of citrus greening, leading to significant income loss for growers and indicating the presence of infected trees. To address this issue, Proofminder has developed an AI-driven model that leverages visual data collected from the fields. This technology enables precise counting of dropped fruit across vast orange plantations encompassing thousands of hectares of land. By analyzing high-resolution images, the AI model detects and quantifies premature fruit drop with remarkable accuracy. The dropped fruits are marked with GPS coordinates, which are provided to workers who can collect them and send them to be juiced. If picked up – thus juiced – in time, dropped oranges still can have economic value.

Figure 1 – Proofminder’s AI model for dropped fruit counting in the orange orchard

Use Case 2: Tree Counting and Classification

Proofminder offers advanced tools for tree counting and classification, categorizing trees in the orchard into living trees, dead trees, and seedlings, while also calculating the number of missing trees. This provides growers with a clear overview of their orchard’s status, helping them assess the extent and location of infestations and reduce spraying costs. Additional benefits include:

Quantified Vegetation Assessment: Based on spectral indexes (stress, water, nitrogen), this assessment helps detect irrigation blockages, provides inputs for regional management, and isolates problematic areas.

Tree Volume Measurement: Canopy size and height measurements are used to calculate the necessary amounts of chemicals.

Proofminder’s technology delivers precision, with a target accuracy of 95%. Data is accessible via an online platform, offering multiple access points, zoomable images, and dynamic analysis layers, along with export options in Excel, CSV, and geospatial formats (KML, Shapefile).

Figure 2 – Proofminder’s AI model for orange tree counting and classification

Conclusion

Citrus greening is a serious disease that has led to a 20% decrease in the fresh citrus fruit market and a 70% decline in orange production for juice and other products in the United States. If you are interested in learning how Proofminder can assist in detecting infected trees and preventing the spread of HLB in your orchard, don’t hesitate to reach out to us.