Florida's fight: The battle against citrus greening for the future of orange juice

The sun is shining and the skies are blue, but there is a palpable anxiety in the Florida orange groves.

A menace is lurking, evading citrus growers’ best attempts to keep it at bay and preserve their livelihood and the world’s favorite breakfast beverage.

The perpetrators are small, no bigger than an eighth of an inch, but they are mighty. The Asian citrus psyllid is responsible for transmitting a bacterial disease called Huanglongbing, better known as citrus greening.                                                                                                                   

What is citrus greening?

As the Asian citrus psyllid feeds on the phloem sap of the citrus trees, the Huanglongbing (HLB) bacteria can be injected. Phloem cells are responsible for transporting nutrients, sugars and metabolites throughout the plant, thus providing the bacteria with a carbon-rich food source.  

Typical citrus greening symptoms include blotchy mottle characterized by random patterns of asymmetrical yellowing on the leaves. In addition, the fruit are often reduced in size, fail to color properly, are misshapen, abscise from the tree prematurely and are bitter in taste. As the disease progresses, root growth is suppressed, there is twig dieback and, eventually, tree mortality occurs. 

Although some varieties of citrus show tolerance to the disease, there is no real resistance. Mature trees that become infected can take years to show symptoms, adding to the complexity of disease management. 

Citrus greening is one of the oldest and most serious citrus diseases. While the disease was first reported in China in 1919, it did not appear in Florida until 2005. 

Why should citrus greening concern you?

All commercial citrus species are susceptible to greening, and it has been reported that over 80 percent of citrus in Florida is infected.

Florida accounts for over 49 percent of citrus production in the U.S. and is one of the world’s largest contributors to the citrus juice industry. As the top agricultural sector for the state, Florida’s citrus industry provides over 76,000 full- and part-time jobs.  

The United States Department of Agriculture (USDA) reports that citrus production in Florida decreased by 16 percent during the 2015–2016 season over the previous year. This is in addition to the continual decline in year-over-year production, with decreases ranging from 4–16 percent on any given year, that the state has been seeing since 2005. 

With the decrease in citrus acreage and the loss in number of production trees, Florida’s economy is being threatened. This decline could mean more sparse grocery shelves for orange juice and higher prices for consumers. 

How is the citrus industry fighting citrus greening?

In an attempt to prevent the spread of the disease, the U.S. government has placed a federal order on the quarantine of citrus plants and plant parts, excluding fruit, from leaving Florida without specific approval and proof of treatment against the Asian citrus psyllid.   

The USDA is also investing millions of dollars into research against the disease. The research spans several studies, including those that look into possible bactericides and finding resistant citrus varieties.

Currently, growers are using scouting, tree removal, nutrition and pesticidal programs to manage the disease. 

Alltech Crop Science is working with growers in Florida, investigating possible ways of combating citrus greening. Research is being conducted to investigate the impact of nutritional inputs as well as to identify how this disease impacts defense genes within infected trees.     

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