What is citrus greening disease?

Symptoms of citrus greening disease

Huanglongbing leaves a mottled, asymmetric yellow pattern on citrus leaves.

(California Department of Food and Agriculture)

The enemy

The bacteria that causes Huanglongbing, or citrus greening disease. (UC Riverside)

Candidatus Liberibacter asiaticus is a bacterium from Asia that colonizes citrus and citrus-related plants. It clogs their nutrition transport system, stunting fruit and causing it to stay green, a phenomenon known as citrus greening disease. Leaves and branches turn a mottled yellow, giving rise to the name Huanglongbing, the Chinese word for yellow dragon disease. Most scientists call the disease HLB.

The friend of the enemy

The Asian citrus psyllid spreads a bacteria lethal to citrus. (Don Bartletti / Los Angeles Times)

Citrus psyllid, or Diaphorina citri, is a tiny mottled-brown insect, about the size of an aphid, that transports bacteria from tree to tree. It feeds on leaves of citrus and other plants in the family Rutaceae, such as calamondin, box orange, Indian curry leaf and orange jessamine, or orange jasmine.

The friend of the enemy's friend

An aphid-sized bug, the Asian citrus psyllid, is found in most of Southern California. (Gina Ferazzi / Los Angeles Times)

Humans spread the psyllid by moving backyard fruit and plants.

The enemy of the enemy

Millions of predatory wasps have been released to combat the Asian citrus psyllid. (Gina Ferazzi / Los Angeles Times)

Tamarixia radiata, a predatory wasp from Pakistan, eats the young of the citrus psyllid, reducing the bug's population and decreasing the opportunities to spread the bacteria. Diaphorencyrtus aligarhensis, another exotic wasp, also preys on the psyllid.

Who you gonna call?

If you suspect psyllid infestation or HLB disease, call the California Department of Food and Agriculture hotline: 1-800-491-1899. More information is available online:

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