Citrus greening disease in Florida: What to know 

Citrus greening disease, scientifically known as huanglongbing, is devastating the international citrus industry. Growers and researchers race to find a cure for the disease because of its rapid spread and ability to render entire groves useless.   

Huanglongbing, or HLB, is the name given to the disease by Chinese researcher Lin Kung Hsiang in 1956, which translates to “yellow dragon disease” or “yellow shoot disease.” This name is a reference to the yellow shoots that grow on infected trees.  

The disease is caused by a bacterium called Candidatus Liberibacter asiaticus. The bacterial infection is spread by the Asian citrus psyllid, a common sap-sucking insect that is native to Asia. Current disease control strategies mainly rely on applying insecticides to kill the insect. 

Citrus greening basics

The bacterium that causes citrus greening disease lives and replicates in the phloem of citrus trees. Phloem is the vascular tissue of plants that transports sugar and nutrients from the production sites to the growing sites of the tree. Gradually, the affected phloem tissue becomes clogged, and the sugar produced in the leaves cannot be transported throughout the tree. Consequently, the sugar molecules accumulate as starch on the chloroplasts of the leaves.

Chloroplasts are the organelles containing the green chlorophyll pigment responsible for capturing sunlight, a primary resource in photosynthesis. As the starch accumulates on the chloroplasts, they die in a process known as chlorosis. This causes the leaves to turn yellow and drop, and the plant becomes unable to produce fruit. Once affected, a tree can remain asymptomatic for several years, serving as a source of bacteria that vectors can spread to other nearby trees.   

Citrus greening in Florida

Citrus greening has become a defining challenge for Florida’s citrus industry over the past two decades. While the vector was first detected in Florida in 1998, the first signs of the disease appeared in 2005. The disease has since spread across virtually all citrus-growing regions, transforming Florida’s agricultural landscape and decimating one of its most iconic crops.

Once citrus greening was introduced to the state, the presence of its widespread and effective insect vector allowed the disease to establish itself quickly and aggressively. Today, both the psyllid and the disease-causing bacteria are found wherever citrus trees grow in the state, from large commercial operations in Central and South Florida to backyard trees in urban and suburban areas.

According to the Florida Department of Agriculture and Consumer Services, Florida citrus land fell from 748,555 acres in 2004 to 274,705 acres in 2024. Groves are abandoned or converted to other uses. Orange production dropped to a fraction of its level in the early 2000s.

While most of the attention has focused on South and Central Florida, HLB has also made its way into North Florida, including parts of the Panhandle. Although commercial citrus operations are less common in this region, the disease has also been confirmed there, particularly in backyard and dooryard citrus trees along the Gulf Coast. Both the psyllid and signs of citrus greening have been documented in counties far beyond the traditional citrus heartland.

The widespread presence of citrus greening has reshaped Florida’s citrus landscape. Scientists continue to search for long-term solutions, including breeding disease-resistant trees and developing biological control methods for the psyllid.

Citrus greening transmission

Citrus greening is caused by a bacterium, which is transmitted from tree to tree by the Asian citrus psyllid. Psyllids become infected with the citrus greening bacterium by feeding on an infected tree. When the psyllid moves on to feed on an uninfected tree, the bacterium is transmitted to the uninfected tree. There have also been documented cases of citrus greening transmitted by grafting, although this form of transmission is far less common.  

While the Asian citrus psyllid is the primary means by which the bacterium can be transmitted from tree to tree, moving an infected tree can introduce the bacteria into an area where they did not previously exist. From there, the Asian citrus psyllid will be able to spread the disease further. 

Symptoms of citrus greening

Citrus greening symptoms can be observed year-round, but they are most visible on fully developed leaves from September to March. Symptoms of citrus greening are more easily observed in shade or on overcast days. When assessing a citrus plant for citrus greening, look out for these signs: 

Populations most vulnerable to citrus greening

Citrus greening disease is capable of infecting virtually all species of citrus, including various species, cultivars, hybrids and citrus relatives. Sweet oranges, mandarins, tangerines and tangelos are the most susceptible to citrus greening. Lemons, grapefruit, pummelos and sour orange trees, while slightly less susceptible, become unproductive when affected by HLB. Mexican lime, trifoliate orange and some trifoliate orange hybrids are more tolerant to HLB disease, and trees may only show some leaf symptoms. 

Citrus greening diagnosis

Diagnosing citrus greening can be challenging because its symptoms often resemble those of nutrient deficiencies or other citrus diseases. However, there are a few key signs that help distinguish citrus greening from other issues. 

A key symptom is the blotchy, mottled yellowing of leaves, typically asymmetrical across the leaf midrib. Affected trees might also exhibit twig dieback, leaf and fruit drop, sparse foliage and small, misshapen, bitter-tasting fruit that often stay green on one end, hence the name “greening.” 

Because visual symptoms can be misleading, a definitive diagnosis requires laboratory testing. Leaf samples are typically sent to certified labs where DNA testing can detect the presence of the bacteria. 

Early detection is important, especially in areas where the disease is not yet widespread, as it can help slow the spread and inform management decisions. 

Citrus greening treatment

There is currently no treatment for citrus greening. Once a tree is infected, it will eventually become unproductive and may even die. 

The most effective way to prevent citrus greening is by stopping the introduction of the Asian citrus psyllid. Currently, the primary method involves expensive chemical controls to reduce psyllid populations.

Citrus greening prevention

Because the disease is now considered endemic in Florida, there are no tolerant or resistant citrus cultivars available. Efforts have shifted from eradication to management, in which growers are investing in strategies to slow the spread and extend the productivity of infected trees. These efforts come with high costs like pest control, enhanced nutrient programs and tree replacement. Researchers have been protecting young trees by using individual mesh bags placed on trees to keep out psyllid infestations.

According to the USDA, these strategies can help limit the spread and prevent the disease:  

• Know the quarantines in your area.
• Buy only USDA-certified citrus plants.
• Don’t move branches, green waste, dead trees or other regulated items out of a quarantined area.
• Don’t mail or transport home-grown citrus fruit or plants out of a quarantined area.
• Commercial nurseries must adhere to strict protocols for relocating citrus nursery stock out of quarantined areas.

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