The Food Journal and Food, Nutrition & Science

An alliance between The Lempert Report and The Center for Food Integrity

The Fight to Save Our Oranges

The Fight to Save Our Oranges

The Food Journal

February 26, 2015

Orange juice has been an American breakfast staple for decades, adding a much-needed pop of color (and vitamin C) to the neutral hues of cereals and pancakes typically found at the morning table. Of the 170.9 million boxes of citrus harvested in Florida during the 2011-2012 growing season, 90 percent was processed into juice. 

Oranges, and orange juice in particular, is big business – the on-tree value of the 2011-2013 Florida crop is estimated $1.35 billion – and extremely important to growers and consumers, alike. But in recent years, the orange juice market has faced some significant hurdles, from the decline of breakfast eaters to the rise of anti-sugar campaigns encouraging people to drink less juice. Now, the industry is facing its biggest challenge yet as they fight a plant epidemic known as “citrus greening.”

What Is Citrus Greening?

“Citrus Greening” is the familiar name for a disease called “Huanglongbing” or just “HLB.” The disease was found in south Florida in 2005 and has since been found in all 32 commercial citrus producing counties. It has also been found in Asia, Africa, South America, and also in North America in the states of California, Arizona and Texas. 

Citrus Greening is a constellation of symptoms caused by a bacterial infection of the plant vascular system. The bacteria spreads from tree to tree by a specific flying insect called the Asian Citrus Psyllid. Early symptoms include vein yellowing and asymmetrical chlorosis, which is an insufficient production of chlorophyll, the green pigment found in plants that is necessary for photosynthesis. Leaves can appear small and upright and appear to be suffering from mineral deficiencies – a condition called “blotchy mottle.” Sometimes poorly developed root symptoms are observed. Also, affected trees produce less fruit, and the fruit may be smaller and even appear lopsided or misshapen. The fruit oftentimes drop from the tree and are unusable, and those remaining on the tree can develop increased levels of bitter compounds. 

How Is Citrus Greening Being Treated?

To date there is no cure. Since the disease is insect vectored, it is almost impossible to control the spread from infected groves. Many groves are just abandoned while some groves burn trees. Others implement an advanced nutrition program applying trace nutrients to the leaves or to the roots, which in some cases has helped infected trees maintain yields. 

Antibiotics and other known drugs or compounds that are safe for human consumption are also being tested for their ability to suppress the bacteria. A number of promising compounds have been identified and are already approved for use on food crops. They could be tested on actual field trees soon but remain expensive and impractical solutions.

Another approach to treatment is through development of new rootstocks. Citrus trees are propagated as a scion (trunk and branches) grafted onto a rootstock. Different rootstocks impart important traits on the scion – think of it as the different way different roots “biochemically-talk” to the branches. Seventeen rootstocks have been identified by the University of Florida that seem to tolerate the HLB infection well, and these are all being tested throughout the state.

“Many approaches have been used to slow or in some cases maybe reverse disease progression. These include nutrition adjustments, insect management, and even the potential use of antibiotics. The biggest issue is the inability to treat a grove of thousands of trees and do so at a realistic cost. Other treatments, such as thermal tents where the temperature of the tree is elevated, show some promise but are unworkable over 60 million trees,” says Dr. Kevin M. Folta, Professor and Chairman, Plant Molecular and Cellular Biology at the University of Florida in Gainesville.

Meanwhile, Folta says researchers at the University of Florida are testing growing citrus in massive screen houses because high-production trees might generate a good crop in a protected environment. And there are different production expectations in play. Instead of growing trees for decades, maybe the next model will grow densely-planted compact trees for a few years, push production, and then replace them with new trees.

How Do Genetic Solutions Fit In To All Of This?

Additional solutions are being sought on many levels, says Folta, from straight up nutrient management to changing the way citrus is grown entirely. For example, new genetics are helping breed trees that don’t get the disease or show symptoms at all. In “transgenic citrus,” trees have a gene added to confer resistance or tolerance to the disease. In fact, there is a gene from spinach that seems to help the tree grow fine with infection. 

“The genes from spinach should not have any effect on the normal growth of the citrus plants. The genes are just providing resistance/tolerance against citrus greening, so the trees can survive and be healthy. The field trials we have in place will confirm this,” says Dr. Erik Mirkov, a Professor with Texas A&M AgriLife Research, and a faculty member in the Department of Plant Pathology and Microbiology in Weslaco, Texas at the Texas A&M AgriLife Research and Extension Center. Mirkov discovered and developed the spinach gene therapy in his lab.

There are other genes that have been installed to help the trees grow or fight infection as well. But opponents of GMOs may not like these options. However, the general consensus amongst researchers around the world who are aware of this disease feel that the ultimate solution will be through applying genetics and biotechnology, says Mirkov.

“The use of genetics and biotechnology in modern breeding methods is becoming more prevalent in the food supply. It will be our job to keep looking for ways to provide consumers with education and assurances that the technology results in foods that are no different from those produced by other breeding methods,” says Mirkov.

Folta adds, “These genetic solutions are all very promising, but there are some big hurdles to overcome in terms of consumer acceptance and massive deregulation. There is a big effort already to question the safety and efficacy of these products even though no fruit have ever been consumed, and they simply contain a gene product that is eaten in any spinach salad,” says Folta.

Mirkov says that the regulatory process is in place and ongoing and will not be an issue provided they perform the rigorous tests towards obtaining the data required. The agencies (EPA, FDA, and USDA) are working well with them, he says, in the deregulation process.

“As we go forward, biotechnology is only to become more important as agriculture strives to deal with new pests and diseases, and overall, increases the amount of food available to feed a growing world population in a sustainable manner,” says Mirkov.

What Does All This Mean For Farmers?

The citrus crop is down 20 percent this year – and every year it gets worse. Fruits are smaller, there are fewer of them, and the disease affects certain varieties more than others. The crisis has cost a billion dollars at least and probably in the neighborhood of 3,000 jobs over 10 years.

“Trees are expensive to replace, and revenue is lost during that time. The high cost of nutrient management and insect control are also factors detracting from a grower’s bottom line. New trees take four to five years to become productive, but those trees are not fully productive for a few more years after that. The disease is slow, and infected trees show symptoms after several years and remain productive through the decline, albeit at lower levels,” says Folta.

Andrew Meadows, Director of Communications for Florida Citrus Mutual, adds that caretaking costs per acre have increased from about $500 before HLB to about $2,000. In other words, production costs have gone through the roof.

Dr. MaryLou Polek, Vice President Science & Technology, Citrus Research Board adds, “Well-managed groves that were provided a good fertilization regime from the start can resist infection better than a poorly managed grove. Strong, healthy trees produce high quality fruit and profitable yields. Poorly managed groves will require greater input to remain profitable. Production costs do increase due to increased insecticide applications, increased survey and monitoring. Growers need to be educated on how to identify the psyllid vector and disease symptoms, so that the disease and the vector can be detected early, and mitigation efforts are minimized. Growers should also be committed to treat when necessary and fertilize regularly to maintain tree health.” (see our full interview with Dr. MaryLou Polek here.)

What Should Consumers Know?

Polek says the greatest threat to citrus growers are residential or backyard trees; the interface between production citrus and residential areas are in greatest danger. Backyard trees can be a source of inoculum (known infected trees), and insect control is limited, so the psyllid vector can very easily thrive in backyard trees. 

“As they feed, they acquire the bacterium. When they fly into an adjacent orchard and feed on healthy production trees, they will transfer the deadly bacterium. Homeowners could be part of the solution by taking care of their trees and allowing Department of Agriculture inspectors entry to their properties to inspect and possibly treat their trees,” says Polek. 

Consumers also need to keep up demand for citrus products, steer away from boutique luxury juices with unsubstantiated health claims and keep consuming healthy citrus juice products. When they can, they should urge action from politicians and drive more research in the public sector in this area, says Folta.

“Consumers are encouraged to become more attached to their farmers and farming in general. We need to remind them that there are farming families down the interstate that are really going through some massive challenges. We’re trying to spread that message, especially so that they’ll understand our genetic solutions if they prove safe and effective,” says Folta.  

“Nobody knows how long it will take to recover, but we are still a $10.8 billion industry supporting 62,000 jobs. We plan on weathering this storm and being here for a long time,” says Meadows. “How can the consuming public help growers face this issue? Buy Florida orange juice.”

Interview on Citrus Greening with Dr. MaryLou Polek, Vice President Science & Technology, Citrus Research Board

What causes Citrus Greening?

Gram-negative bacteria have been associated with huanglongbing (HLB), also known as yellow shoot disease and citrus greening. To date, no one has been able to maintain a pure culture of these bacteria in the laboratory making it difficult to study. Three species have been identified, each named for the geographical location where they were detected: Candidatus Liberibacter asiaticus (CLas – China, India), Ca. Liberibacter aficanus (CLaf – Africa), and Ca. Liberibacter americanus (CLam – South America/Brazil). The term Candidatus is Latin for a candidate species, one that has not been cultured. These bacteria are always associated with phloem tissue of their host plant. Ca. L. asiaticus is the species that is currently responsible for HLB in the United States.

Is there a cure for it? If not, what do you have to do when trees or groves become infected?

There is no known cure for this disease; nor are there any known resistant varieties or cultivars. Because the causal agent resides within the vascular system (phloem) of the plant, methods to destroy the bacteria would also be detrimental to the plant. In Brazil, they recommend a three prong response that includes the removal of inoculum (known infected trees), continuous applications of pesticides to control the insect vector, and planting and replanting with certified, disease-free nursery stock. Florida is pursuing a process called thermotherapy in which a huge tent is placed over a tree in a grove to raise the temperature within the tent to a level that is lethal to the bacteria. There are variations in this method including using steam heat to fill the tent for a short period of time or long durations of solar heat.

If you have to destroy an entire grove do you have to treat the soil before replanting?

If the disease is detected early, there is no need to destroy an entire grove. Soil does not require treatment prior to replanting since the bacteria requires the phloem environment to survive. The bacteria does reside in the roots of a plant, so it would be advisable to be sure when you remove a tree, you remove the roots as well.

If you have to replant, how long does it take before the trees produce oranges?

Just like any new planting, it depends on the variety, climatic conditions. Typically young trees will produce fruit three to five years after planting. Citrus is a perennial, woody plant and requires several years to mature, unlike an annual crop such as tomatoes.

How much does all this cost a grower/family? What kind of investment do they have to make in time and money?

Well-managed groves that were provided a good fertilization regime from the start can resist infection better than a poorly managed grove. Strong, healthy trees produce high quality fruit and profitable yields. Poorly managed groves will require greater input to remain profitable. Production costs do increase due to increased insecticide applications, increased survey and monitoring. Growers need to be educated on how to identify the psyllid vector and disease symptoms, so that the disease and the vector can be detected early and mitigation efforts are minimized. Growers should also be committed to treat when necessary and fertilize regularly to maintain tree health. 

How much of the Florida crop is impacted, and how long will it take to recover?

Scientists believe that 100 percent of all citrus groves in Florida contain infected trees. The Florida industry went from about a million acres to about 500,000 acres since the detection of greening and the canker eradication program. The crop estimate for this year is 1,300,000 boxes. The time for recovery is unknown at this time. Smaller, low efficiency processing plants have closed and jobs have been lost. There has been an increase in pre-harvest fruit drop which decreases yield, and there is less fruit to be processed into juice. 

What options seem the most promising for a future cure?

The most promising option for California is the development of early detection methods and the removal of diseased trees before visual symptoms appear. Breeders are very busy screening citrus varieties and citrus relatives for disease resistance and/or tolerance; but this is for the long term. Antimicrobials are being developed and evaluated in Florida. Engineers are improving thermotherapy methods in which steam heat is applied to field trees to kill populations of bacteria within the tree. This method seems to increase the productivity/life expectancy of trees for about three years. A new technology called RNAi is being delivered into trees by using a plant virus that naturally infects citrus, called citrus tristeza virus (CTV). CTV will release small molecules of RNA that interfere will normal cell processes such as vital enzyme production. 

What do you most want consumers to know about the industry, what it needs and what it is doing?

The greatest threat to citrus growers are residential or backyard trees; the interface between production citrus and residential areas are in greatest danger. Backyard trees can be a source of inoculum. Insect control is limited so the psyllid vector can very easily thrive in backyard trees. As they feed, they acquire the bacterium. When they fly into an adjacent orchard and feed on healthy production trees, they will transfer the deadly bacterium. Homeowners could be part of the solution by taking care of their trees and allowing Department of Agriculture inspectors entry to their properties to inspect and possibly treat their trees. 

What other areas in the U.S. and around the world face this problem?

All citrus production areas worldwide are in danger because of this disease. It was first identified in China and India in the early 20th century. It is also present in South Africa, Vietnam, Eastern Asia, South America, Central America, and Mexico. The disease was first identified in Florida in 2005 and has spread throughout the southwest United States into Louisiana, Mississippi, Alabama, Texas, and a single tree in California that has been removed. 

How can the consuming public help growers facing this issue?

Continue to buy citrus and citrus products! If they want to plant a citrus tree in their yard, they should buy plants from a certified nursery where plants are inspected regularly and started from a disease-free source. They should never share budwood or graft onto their trees using material from their “friend.” Hobbyists or immigrant communities often unknowingly bring infected material from infected areas. perhaps because they moved from Florida and brought their potted citrus trees or packed budwood in their suitcase from their homeland. Once these get into the environment, hungry psyllids can feed on these infected trees and transmit the bacteria to production trees.