Citrus Greening (HLB)
Candidatus Liberibacter species
A fatal bacterial disease of citrus, spread by a tiny insect, that turns leaves blotchy yellow, makes fruit small, green, and bitter, and eventually kills the tree. Citrus greening, or huanglongbing, is the most serious citrus disease in the world and has devastated citrus in Florida and elsewhere; there is no cure.
🔎 How to spot it
The classic leaf sign is a blotchy, asymmetrical yellow mottling that does not match on the two sides of the leaf midrib, along with yellow veins and a thin, dying-back canopy. Fruit are small, lopsided, and poorly colored, staying green at the bottom even when ripe, often dropping early, and tasting bitter with aborted seeds. The whole tree slowly declines over a few years.
🥀 Damage it causes
The bacterium clogs the food-conducting tissue of the tree, so it loses vigor, drops fruit prematurely, yields small, misshapen, bitter fruit that is unfit for eating or juice, and gradually dies branch by branch. Once a tree is infected it cannot be cured and will decline and die, and it serves as a source to infect other trees nearby. Entire plantings can be lost.
🔬 What causes it
Citrus greening is caused by the bacterium Candidatus Liberibacter, which lives in the food-conducting tissue of the tree and is spread from tree to tree by the Asian citrus psyllid, a small sap-feeding insect, as well as on infected grafting material. The bacterium cannot yet be grown in culture or cured, and the psyllid carries it efficiently, so the disease spreads quickly where the insect is present.
🛡️ Prevent it
Plant only certified disease-free citrus from a reputable nursery, and learn to recognize and control the Asian citrus psyllid that spreads the bacterium. Inspect trees regularly for blotchy mottle and report suspected greening to agricultural authorities in quarantine areas. Remove and destroy infected trees promptly so they cannot infect neighbors, and keep trees vigorous to prolong productivity.
🧯 If it is already here
There is no cure; infected trees should be removed and destroyed to protect other citrus, and the realistic strategy is to delay infection by controlling the psyllid vector and planting clean stock. Where trees are already infected, careful nutrition, irrigation, and pH management can keep them productive somewhat longer but cannot save them. Vector control and clean planting material are the only real defenses.
💡 Good to know
The asymmetric, blotchy yellow mottling on the leaves and the small, green-bottomed, bitter fruit are the signatures that distinguish greening from a simple nutrient deficiency. Because a tiny insect spreads an incurable bacterium, the whole battle is fought against the psyllid and against moving infected plants. Greening is under quarantine in many citrus regions.
🌱 Plants it affects
14 plants in the library can be affected by this problem
For educational and informational purposes only. Disease management advice is general guidance drawn from university cooperative extension sources; always identify a problem positively and read and follow the label on any product before use, especially around food crops, children, and pets.