Citrus Chlorosis: Symptoms, Causes, and Prevention

Chlorosis is a common disease in citrus trees, manifesting as yellowing leaves due to a chlorophyll deficiency. This weakens trees, reducing their ability to photosynthesize and, consequently, their productivity. Identifying the early signs of chlorosis and understanding its causes is essential to protecting your citrus trees and ensuring abundant, high-quality harvests.

Symptoms of Citrus Chlorosis

Symptoms of citrus chlorosis are primarily visible on the leaves, but they also affect fruit size and quality. Here are some telltale signs to look out for:

• Yellowing leaves : The most common symptom is yellowing between the veins, which remain green. This characteristic pattern is easily recognizable.
• Reduced leaf size : Affected leaves are often smaller than normal and may have abnormal shapes.
• Downward Leaf Curling : In addition to their reduction, leaves affected by chlorosis tend to curl downward.
• Smaller Fruits : Trees affected by chlorosis generally produce smaller fruits, with thinner, smoother bark.
• Premature fruit drop : Affected citrus trees may also lose their fruit prematurely, reducing the harvest.

Citrus Variegated Chlorosis (CVC)

In addition to the classic chlorosis symptoms, there is a specific type of chlorosis called citrus variegated chlorosis (CVC) . This variant has more severe symptoms:

• Raised and gummy lesions : Raised areas develop on the underside of the leaves, and these areas often become gummy.
• Twig dieback : Branches begin to die back, gradually weakening the tree.
• Fruits with hardened rinds : Fruits have harder than normal rinds and ripen faster than expected, which may compromise their quality.

Citrus variegated chlorosis is caused by a bacterium called Xylella fastidiosa , a serious threat to citrus trees in many parts of the world.

Causes of Citrus Chlorosis

The causes of chlorosis can vary depending on environmental conditions and cultural practices. The most common factors include:

• Iron deficiency : Iron is essential for the synthesis of chlorophyll. A deficiency of iron, either due to a lack of this element in the soil or due to a blockage of its assimilation, can lead to chlorosis.
• Soil pH too high : A high pH (often due to excess limestone) prevents citrus roots from absorbing iron, even if it is present in the soil.
• Soil conditions : Soil that is too wet or too dry disrupts nutrient absorption, causing deficiencies. Additionally, watering with very hard water can exacerbate the problem.
• Variegated chlorosis : Unlike other types of chlorosis, variegated chlorosis is caused by bacteria rather than nutrient deficiency. Xylella fastidiosa colonizes the xylem vessels, blocking the flow of water and nutrients.

Prevention of Citrus Chlorosis

Prevention is crucial to prevent chlorosis from affecting your citrus trees. Here are some effective measures to protect your trees:

• Improve soil drainage : If your soil is too wet, it is important to ensure good drainage to avoid root asphyxiation.
• Mulch trees : In case of drought, mulch the base of the trees to maintain humidity and protect the roots from sudden changes in temperature and humidity.
• Amend the soil : Regularly adding organic matter, such as compost or well-rotted manure, improves soil structure and its ability to retain nutrients.
• Choosing suitable rootstocks : If you are planting citrus fruits in calcareous soil, choose rootstocks that are resistant to calcareous soils to reduce the risk of chlorosis.
• Monitor Soil pH : Maintaining the proper pH is essential for your citrus trees. Use limestone to neutralize acidic soils or sulfur to correct alkaline soils.
• Feeding Potted Plants : If you grow your citrus trees in pots, be sure to feed them regularly with balanced fertilizers to compensate for the lack of nutrients due to limited space.

Means of Combating Chlorosis

If chlorosis is already present in your orchards, it is important to act quickly to control the situation. Here are some effective control measures:

• Iron chelate treatments : These treatments are particularly effective in correcting iron deficiencies, and they are authorized in organic farming.
• Nettle Manure : Apply a 10% diluted nettle manure. This treatment, rich in iron and minerals, helps correct chlorosis naturally.
• Anti-chlorosis foliar fertilizer : Spray a specific foliar fertilizer every three weeks during the growing season to strengthen the leaves and correct nutrient deficiencies.

However, it's important to note that these solutions are often temporary. To resolve the problem long-term, it's essential to identify and treat the underlying cause of chlorosis, whether it's a soil pH imbalance, poor irrigation, or a nutritional deficiency.

Conclusion: Protecting Your Citrus Fruits from Chlorosis

Citrus chlorosis is a significant challenge for growers, but with proper preventative measures and careful soil management, it can be controlled. Regularly monitoring the condition of your trees, amending the soil according to its needs, and using specific treatments are key strategies for ensuring the health and productivity of your citrus trees.

To ensure abundant, high-quality harvests, adopt preventative practices and promptly treat any signs of chlorosis. By doing so, you can protect your citrus trees from this disease and keep your orchards healthy for years to come.

FAQs

• What are the symptoms of chlorosis in citrus trees? Symptoms include yellowing of leaves between the veins, reduced leaf size, leaf curling, and smaller fruit.
• How is citrus variegated chlorosis (CVC) diagnosed? Citrus variegated chlorosis presents with swollen lesions under the leaves, twig dieback, and fruit with hardened rind.
• What are the main causes of citrus chlorosis? Chlorosis is often caused by iron deficiency, high soil pH, unsuitable soil conditions, or watering with very hard water.
• How can citrus chlorosis be prevented? It is important to improve soil drainage, amend with organic matter, monitor soil pH, and choose suitable rootstocks.
• Is there a cure for chlorosis? There is no permanent cure for chlorosis. Temporary treatments such as iron chelates or foliar fertilizers can be applied, but the underlying cause must be identified and treated.
• Why is citrus variegated chlorosis more dangerous? Variegated chlorosis is caused by the bacterium Xylella fastidiosa, which causes more severe symptoms and can be more difficult to control than other forms of chlorosis.