Citrus Greening (HLB)
Written 2008; edited January 2013; source updated March 2014
Huanglongbing (also known as HLB or citrus greening) is a disease affecting citrus production all over the globe. Citrus greening affects all citrus cultivars and causes tree decline, a serious threat to Florida's citrus industry.
The disease is believed to be caused by the bacterium Candidatus Liberibacter asiaticus. The Asian citrus psyllid (Diaphorina citri Kuwayama) transmits the bacterium and is found throughout Florida.
Asymmetrical yellowing of the leaves and leaf veins (referred to as "blotchy mottle") is an early symptom of citrus greening. This mottling can be confused with symptoms of mineral deficiencies.
Mottling may first occur on a single shoot or branch, but will usually spread throughout the tree over a few years.
Later symptoms of citrus greening include twig dieback and decreased fruit production. The fruit a tree does produce is usually small, lopsided, and underdeveloped. Fruit will often drop prematurely from infected trees.
Regularly scout citrus for signs of greening. Scouting should be done at least four times a year, or more in areas known to have infected trees. October through March is the best time for scouting, but symptoms can be present at other times of the year.
Scouting methods can be found in Scouting for Citrus Greening.
Citrus greening cannot be diagnosed by symptoms alone. First, use an iodine-based starch test on suspected trees. This test identifies if the tree is likely to have HLB but is not a positive diagnosis (See: An Iodine-Based Starch Test to Assist in Selecting Leaves for HLB Testing).
Then samples of possibly infected trees can be sent for a polymerase chain reaction analysis (PCR) diagnosis, which is the only way to positively identify citrus greening.
Both the Southern Gardens Diagnostic Laboratory or the Southwest Florida Research and Education Center in Immokalee offer PCR diagnosis. Submission forms and information are available at the Citrus Research and Education Center (CREC) Extension.
HLB is difficult to manage and can continue to spread through Florida citrus since the Asian citrus psyllid is well-established.
Refer to the Florida Citrus Pest Management Guide for current reccomendations for managing citrus greening.
Adapted and excerpted from:
R. Brlansky, et al., 2014 Florida Citrus Pest Management Guide: Huanglongbing (Citrus Greening) (PP-225), Plant Pathology Department (rev. 09/2013).
Related Sites & Articles
- Hot Topics
- Managing Citrus Greening
- UF/IFAS Publications
- Asian Citrus Psyllid, Diaphorina citri Kuwayama
- Economic Impacts of Citrus Greening (HLB) in Florida, 2006/07–2010/11
- The Effects of Huanglongbing on Florida Oranges
- Iodine-Based Starch Test for Selecting for Citrus Greening
- Sampling for Asian Citrus Psyllid in Florida Citrus Groves
- Scouting for Citrus Greening
- UF/IFAS Sites
- Citrus Greening Database
- Citrus Greening