Orange trees can be heavily affected by insects (mainly aphids) and also by fungal, bacterial and virus diseases.
Aphids (mainly Aphis spiraecola) are small flies that are fed with the underside of leaves, often resulting in the curl of citrus leaves. This by itself is not a great damage, because the yield of a citrus tree is not greatly affected by the curling of leaves. However, aphids can also transmit the tristeza virus. Aphids mainly affect young trees with soft leaves, and their population rapidly decreases as the tree matures and the leaves harden.
Major bacterial diseases of citrus
1.) Pseudomonas syringae (Blast): It affects leaves, shoots and fruits. Black spots appear on the petiole and they expand rapidly. A common symptom is that leaves curl or turn black and die, while black spots may also appear on the fruit. After consulting a licensed agronomist, farmers often use a copper fungicide.
2.) Xanthomonas citri: It causes citrus canker. The most common symptom is spots that appear on leaves and fruits. Infected trees suffer from defoliation and premature fruit fall. The pathogen affects young leaves, tender shoots and young fruit. Unfortunately, it can be quickly spread from infected areas of the tree to non-infected areas through rainwater, resulting in the premature fall of leaves and fruits.
Major fungal diseases of citrus
1.) Thielaviopsis basicola: It causes Black Root Rot. Black spots appear on the roots, which may finally turn entirely black.
2.) Penicillium digitatum: It causes Green Rot or Mould. The fruit rots, shrinks and finally collapses.
3.) Diaporthe citri: It causes Melanose. Small dark spots appear in leaves, young stems and fruits. The pathogen causes premature leaf fall and fruit rot.
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14.) Orange Tree Diseases and Pests
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