Citrus greening is a global problem. It has infected or will soon infect citrus trees in most citrus-producing countries. The disease causes reduced production, increases in planting and maintenance costs, loss of market value, and ultimately lower returns for growers. Most citrus producers are very concerned about the effects of Citrus Greening (Citrus Greening – CG).
It is a highly contagious soil-borne fungus that attacks many types of citrus trees. When left untreated, it weakens the tree and makes it more susceptible to other diseases or pests like anthracnose, scale insects, and twig girdling. As you might already know, this disease attacks leaves and stems causing yellow mottling on the leaves.
It also affects root systems making the tree more vulnerable to other diseases as well as harsh weather conditions. If not controlled fast enough, it can wipe out entire groves within a few years making reforestation cost-prohibitive.
knowledge of available control methods and their potential efficacy against it, commitment from your farm team towards implementing effective measures to prevent the spread of this disease as well as access to funding for ongoing monitoring and maintenance costs all of which are time-consuming tasks with no single solution that can be used universally by all citrus growers worldwide.
What is Citrus Greening?
Citrus greening is a disease that affects citrus trees. It is caused by a soil-borne fungus. Symptoms begin as the mottling of the leaves. This then progresses to yellowing and eventual brown discoloration.
Leaves may also become stunted and distorted. The cause of citrus greening is a fungus that is transmitted by aphids and other insects. The fungus is an obligate pathogen, meaning that it cannot survive in the presence of a pathogen that will kill it.
In order for it to survive, citrus trees must have a diseased host nearby. So, the fungus is actually a parasite that lives on its host. In the case of citrus greening, there are multiple host trees that carry the fungus. Trees include oranges, grapefruit, and tangerines, but mostly oranges. Hybrid orange trees may also be infected, but the disease is not nearly as severe on them.
CG symptoms and biology
- Symptoms: Mottling on the Leaves – Yellowing and eventual brown discoloration
- Disease Host: Many citrus trees, including oranges, grapefruit, and tangerines
- Transmission: Fungus is transmitted by aphids and other insects.
- Diagnosis: By observing symptoms in the field and doing laboratory tests on samples
- Control: Prevention – Early detection and control of aphids and other vectors are the main tools for control of citrus greening.
- Treatment: There is no cure for citrus greening and control measures are only for prevention and slowing down the progression of the disease.
Available control measures for CG
- Orange Suckers – Suckers are tiny shoots that grow on orange trees.
- Orange Bloat – Orange Bloat is a condition where the orange fruit is swollen and discolored.
- Orange Scab – Orange Scab is a fungus that causes the orange leaves to die. The tree recovers in time.
- Yellow Twig Blight – Yellow Twig Blight is caused by fungi that infect the branches of orange trees. These branches die and fall off.
- Citrus Huanglongbing – Citrus Huanglongbing is a bacterial disease that infects citrus trees in Asia.
- Other Control Measures – Other control measures for citrus greening include making sure that trees have good drainage and that irrigation water has a low salt content.
The commitment of the farm team toward effective prevention measures
Effective prevention of citrus greening requires commitment from all the stakeholders on your farm from the farm manager, growers, and workers to the suppliers and importers. They need to be informed about the risks of CG infection and how to prevent it. They also need to be trained on how to implement effective control measures.
This includes awareness about the symptoms and biology of the disease, and how to identify the vectors and manage them. They also need to be familiar with the need to use biocontrol agents. Biocontrol agents are beneficial organisms that are used to manage exotic invasive species.
Best practices for citrus greening prevention include the following:
- Clean and wash all tools, equipment, and clothes before and after work to prevent the spread of pathogenic organisms.
- Keep all tools, equipment, and clothes clean and dry.
- Keep all groves and fields free of fallen trees, branches, and other debris.
- Inspect all trees and branches for signs of disease and remove them.
- Plant only healthy citrus trees.
- Plant no more than one orange tree per five-acre plot.
- Maintain a five-acre per orange tree plot minimum.
Funding required for a successful long-term management program
Preventing citrus greening is best done by planting only healthy trees. To do this effectively, reliable data about which varieties are healthy and which are not is needed. Healthy trees are those that have resistance to disease. Maintaining a healthy tree population means making sure that new trees are only planted from healthy stock.
Healthy trees are also those that have been maintained so that they are not being over-thinned or over-mature. It also means that they are not being under-mature. Many growers may try to make up for low profits by planting more trees. This is not a good practice as it increases the risk of losing the whole plantation due to severe weather effects.
In addition, planting more trees increases the cost of care and maintenance. To properly manage citrus or other agricultural farms, revenue cannot be gained simply by planting more. Effective management strategies for citrus greening prevention must include a funding source for long-term management programs.
Citrus greening is one of the most devastating diseases affecting citrus crops worldwide. It is caused by a soil-borne fungus and can kill trees within a few years. The only effective way to fight it is by planting only healthy citrus trees and maintaining a healthy tree population.
To prevent citrus greening, you must clean and wash all tools, equipment, and clothes before and after work to prevent the spread of pathogenic organisms. Keep all tools, equipment, and clothes clean and dry. Keep all groves and fields free of fallen trees, branches, and other debris. Inspect all trees and branches for signs of disease and remove them.
Plant only healthy citrus trees. Maintain a five-acre per orange tree plot minimum. These practices will help you fight this devastating disease and maintain a healthy citrus tree population.