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Huanglongbing (HLB or Citrus Greening)

Citrus huanglongbing (HLB), previously called citrus greening disease, is one of the most destructive diseases of citrus worldwide. HLB is one of the most devastating diseases of citrus, and since its discovery in Florida in 2005, citrus acreage in that state has declined significantly. 

HLB is caused by unculturable phloem-limited bacteria. There are three forms of greening that have been described: the African form produces symptoms only under cool conditions and is transmitted by the African citrus psyllid Trioza erytreae. The Asian form prefers warmer conditions and is transmitted by the Asian citrus psyllid Diaphorina citri. 

A third American form transmitted by the Asian citrus psyllid was discovered in Brazil.  In North America, HLB is known to occur in Florida Louisiana, South Carolina, Georgia, Cuba, Belize, and the Eastern Yucatan of Mexico. 


The HLB bacteria can infect most citrus cultivars, species, and hybrids, and even some citrus relatives. Leaves of newly infected trees develop a blotchy mottle appearance. On chronically infected trees, the leaves are small and exhibit asymmetrical blotchy mottling

Fruit from HLB-infected trees are small, lopsided, poorly colored, and contain aborted seeds. The juice from affected fruit is low in soluble solids, high in acids, and abnormally bitter. The fruit retains its green color at the navel end when mature, which is the reason for the common name "citrus greening disease."

This fruit is of no value because of poor size and quality. There is no cure for the disease and rapid tree removal is critical for prevention of spread.

Taken from: Center for Invasive Species Research, University of California Riverside

Text provided by Elizabeth Grafton-Cardwell, Extension Specialist of Entomology 
Photos courtesy of Michael Rogers, University of Florida

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