Orange Tree: How to Identify and Treat Its Diseases and Parasitic Pests?

What are the most common parasitic pests of orange trees?

Like many fruit trees, orange trees attract their share of unwanted little visitors. These parasites, often tiny, can nevertheless cause significant damage if not detected and treated in time. This is even more true if you grow your orange tree in a pot. In winter, when confined to a greenhouse or conservatory, it becomes relatively susceptible to insect attacks. However, orange trees grown in open ground are not exempt from diseases.

Aphids

These are certainly the most common pests on orange trees. These small, soft-bodied insects, most often black or green in colour, pierce the leaves, particularly young shoots, and suck the sap. They secrete honeydew, which ants feed on.

• Symptoms: The orange tree’s leaves curl, deform, and turn yellow; flower buds abort; growth is weakened; and there is a risk of sooty mould appearing.
• Treatment: A spray of garlic decoction or a mixture of black soap and water, possibly with added vegetable oil, is often enough to rid the tree of these intruders. You can also introduce ladybird larvae or lacewings. In case of a severe infestation, a natural pyrethrum-based insecticide may be necessary.
• Prevention: Regular monitoring of the orange tree allows for quick action.

Scale Insects

Another dreaded parasite of the orange tree is the scale insect, another sap-sucking insect that feeds on the tree’s tissues. They appear as small white, brown, or cottony shields attached to stems and leaves, usually on the underside or in the axil. Scale insects thrive particularly in warm, humid environments.

• Symptoms: The orange tree’s leaves curl, and entire branches eventually dry out.
• Treatment: Orange trees grown in open ground can be sprayed with a strong jet of water to dislodge the scale insects. For potted orange trees, you can first scrape the infested areas with a cotton bud dipped in 90°C alcohol, then spray a solution of black soap and vegetable oil in a litre of water.
• Prevention: Again, systematic monitoring of your tree will allow you to intervene quickly. Also, remember to ventilate your greenhouse or conservatory.

Citrus Leaf Miner

The citrus leaf miner (Phyllocnistis citrella) is a nocturnal moth, silvery white in colour, which produces yellowish larvae. These attack the leaves, tunnelling through them in serpentine-shaped mines. This butterfly appears in April, and several generations can occur in a single season. The citrus leaf miner mainly attacks orange trees in open ground, in Mediterranean regions and Corsica.

• Symptoms: The leaves are marked with silvery, then black, mines. The leaves shrivel, dry out, and fall. The orange tree’s growth slows.
• Treatment: There is no effective treatment to eliminate this insect, but pheromone traps can capture males and thus limit mating. Otherwise, as soon as a leaf is visibly attacked, it is recommended to remove it.
  

  Symptoms of citrus leaf miner presence

Mediterranean Fruit Fly

When the orange tree bears fruit, beware of the Mediterranean fruit fly (Ceratitis capitata), which lays its eggs under the fruit’s epidermis. Upon hatching, the larvae tunnel into the oranges and feed on the pulp, rendering the fruit inedible.

• Symptoms: The oranges are punctured and wormy, making them unfit for consumption.
• Treatment: Regular collection of fallen fruit and pheromone traps to capture males remain the most effective treatment and prevention methods.
  

  Mediterranean fruit fly

How to identify and treat the most common diseases in orange trees?

Certain diseases are more common among orchard growers, but your orange tree planted in the ground (less frequently in pots) can also be affected. Note that Huanglongbing (also known as Citrus greening), a devastating disease for citrus trees, is currently only found in Asia, America and Africa, but not yet in European territory.

Phytophthora Gummosis

This is a serious and feared disease caused by the fungi Phytophthora citrophthora or Phytophthora parasitica, which affects the trunk and roots of the orange tree, particularly at the base. This condition is often triggered by excess moisture or poor planting conditions, such as poorly drained soil.

• Symptoms: This fungal disease manifests as amber gum oozing, sometimes accompanied by scaly cracks in the bark. The tree then shows signs of general weakness, including yellowing foliage, withering branches, fruit rot, and stunted growth.
• Treatment: If infected, pruning and/or cleaning the affected areas and applying an organic fungicide like Bordeaux mixture can help contain natural spread.
• Prevention: Ensuring good soil drainage and avoiding injuries to the collar are crucial. Regular pruning to remove diseased branches, followed by the application of a healing sealant, is also recommended.

Sooty Mold

Sooty mold, or black mold, is a direct consequence of aphid or scale insect infestations. A black fungus develops on honeydew, forming a sooty layer on leaves and stems, blocking photosynthesis.

• Symptoms: Leaves become sticky, then yellow. Growth slows, and the tree becomes unsightly.
• Treatment: The priority is eliminating the responsible pests. A simple wash with clean water or a bit of black soap often removes the black layer.

Citrus Canker

Sometimes called citrus bacterial canker, this disease is caused by the bacterium Xanthomonas citri. Particularly severe, it spreads rapidly through water splashes, contaminated tools, or insects, affecting leaves, fruit, and branches.

• Symptoms: Brownish, slightly sunken spots on leaves, branches, and fruit, often surrounded by a yellow halo. Leaves drop, and fruit becomes deformed and falls prematurely.
• Treatment: Remove infected parts and, if necessary, severely affected trees to prevent orchard-wide contamination.
• Prevention: Avoid overhead watering. Protect orange trees from wind and always use sterilised tools.

Mal Secco

This fungal disease, caused by Phoma tracheiphila, affects leaves, branches, or even the entire tree.

• Symptoms: Leaves discolour, starting at the veins, then wilt and dry. Branches die back. When cut, orange staining is visible in the wood. In severe cases, the orange tree dies.
• Treatment and Prevention: No effective treatment exists, so focus on preventive measures like tool sterilisation, pruning and soil work in dry weather, and avoiding injuries.

Citrus Brown Rot

Brown rot is a fungal disease caused by Monilinia, primarily attacking fruit. It thrives in humid climates.

• Symptoms: Oranges develop brown spots covered in white mould. Leaves yellow and drop prematurely.
• Prevention: Essential, as treatments are ineffective and impractical for fruit. Prevent by sealing tree wounds with sealant, reducing humidity, removing mummified fruit, and pruning infected parts.

Citrus Tristeza Virus

This virus, mainly spread by the brown citrus aphid, is particularly devastating. It attacks the tree’s vascular tissues, disrupting sap flow.

• Symptoms: Leaves and fruit become stunted and deformed, may show mottling, trunk cracks appear, the tree weakens and dies.
• Treatment and Prevention: No cure exists once the virus takes hold. Prevention is key—choose resistant rootstocks, monitor for aphids, and remove infected trees.

Prevention and good cultivation practices

By adopting a few simple practices in the garden, it’s possible to avoid most diseases and significantly limit parasitic invasions. Here are the good habits to adopt daily:

• Soil maintenance and controlled watering: Well-drained soil, neither too dry nor waterlogged, is essential. Using organic mulch (such as wood chips or dead leaves) helps retain moisture without excess. For watering, it’s better to water less frequently but deeply, especially during hot periods.
• Regular pruning and branch aeration: Pruning promotes air circulation and light penetration, two factors that naturally hinder fungal growth. It also limits areas where parasites can hide. Gentle pruning in late winter or early spring is best, and don’t forget to disinfect tools before and after each use.
• Monitoring and early detection: A regular walk around an orange tree helps spot the first signs of infestation early.
• Use of natural treatments: If needed, natural solutions abound: black soap against aphids and scale insects, nettle fertiliser or horsetail to strengthen the tree’s defences… These gentle remedies respect the garden’s ecosystem while being remarkably effective when used correctly.