Saving organic citrus: Research finds silver lining amid devastating statistics
Ben McLean III
This article was originally published in February 2018
When I first wrote an article for PCC about citrus greening disease two years ago, crop conditions were already bad. Unfortunately, the damage and crop loss from citrus greening in Florida has only worsened.
The current U.S. Department of Agriculture estimate for the 2017-2018 season shows Florida’s orange crop down to only 46 million boxes, a significant decline from 2009’s harvest of 166 million boxes. Some of this loss is due to Hurricane Irma but, prior to Irma, statistician Elizabeth Steiger had estimated a crop of only 75 million boxes – a paltry projection compared to the more than 200 million box harvests of the early 2000s. Current projections do not forecast any improvement.
Thankfully, due in part to funding from PCC through The Organic Center, important discoveries are being made for best practices on how to cope with and even cure this industry-wide debilitating disease. Recent research into resistant varieties, organic probiotics and surviving trees has given some hope for the long-term future of citrus production, especially for organic citrus.
A history of citrus greening
Citrus Greening disease first appeared in 1919 in southern China, spreading to South Africa in 1928 and causing widespread damage by the 1980s. The disease reached South America in the early 2000s, arriving in Florida in 2005. The widespread and damaging effects of citrus greening have also been felt across the Caribbean, Central America and Mexico. Recently, infected trees have also been found in Texas and in residential areas of Southern California.
Citrus greening is spread by a tiny insect, the Asian citrus psyllid, that infects the trees by injecting deadly bacteria from its gut into the tree when feeding upon its leaves. Once infected, the bacteria spreads to the tree’s root system, setting in motion a series of devastating symptoms that include premature fruit drop, small misshapen fruit and twig dieback. These misshapen and bitter fruits are unsuitable for sale and most infected trees die within a few years.
Citrus greening has become endemic across Florida and likely has caused roughly $5 billion in damage and the loss of up to 10,000 jobs. University of Florida researchers predict that citrus production will fall to only 27 million boxes in 2025 if a cure isn’t found, and current trends suggest this decline could occur even earlier. The grim reality of rising production costs and plummeting yields leaves most citrus growers facing a harsh reality.
Research to control and cure
Recent research supported by PCC and The Organic Center has uncovered six helpful and exciting developments to combat and potentially cure citrus greening:
- Controlling psyllid populations. Mycotrol is a product containing a beneficial organic fungus that reduces Asian citrus psyllid populations when applied monthly to citrus foliage. While not powerful enough to be a stand-alone treatment, Mycotrol provides organic citrus growers with another tool in their arsenal against this insect. Best results were found in the fall and winter dormant seasons, demonstrating the potential to significantly reduce overwintering insect populations. (Dr. Michael Rogers, University of Florida, 2016)
- Antibacterial therapies are less productive. Researchers were not able to overcome advanced states of the disease with any antibacterial therapies or products. Based on these findings, researchers can redirect their focus to the identification of disease-resistant genetics. (Dr. Ron Brlansky, University of Florida, 2016)
- Tolerant varieties have shown disease resistance. Through traditional breeding methods, researchers at the University of Florida have developed a mandarin hybrid, the “Sugar Belle,” a tangerine-tangelo cross that shows promise to withstand the disease. An appealing variety for both fruit and juice, the Sugar Belle can be used to help breed other resistant citrus varieties.
- Beneficial microbes may unlock a cure. Newly discovered populations of microbes found in disease-surviving trees could provide probiotic inoculations to help citrus trees fight off the disease. Natural products produced by these microbes may have the potential for use as antimicrobial formulations against the citrus greening pathogen. (Dr. Caroline Roper, University of California, Riverside, 2017)
- Resistant rootstocks are performing well. The promise of resistant rootstocks probably provides the most advanced area of disease research. Resistant rootstocks have been performing well in limited trials and are now being tested on a much larger scale. For those not familiar with citrus production, the rootstock is the base material on which the new desired variety is grafted. In comparison to seedlings, the benefits of rootstocks include earlier maturity and enhanced productivity. (Dr. Jude Grosser, University of Florida)
- Nutrient balance affects tree health. Adequate nutritional levels of boron, manganese, magnesium and calcium have been shown to help reduce infection in trees. As always, balanced nutrition within the citrus production program has been and will continue to be a valuable and important tool to keep the trees healthy. (Dr. Jude Grosser, University of Florida)
- Resistant varieties can help trees recover. Inarching is a grafting technique that imparts disease resistance from a rootstock to a scion (the upper part of the tree). Experiments show that resistant varieties of limes and other citrus relatives can provide rehabilitation for infected trees, as well as potential resistance and immunity to young trees not yet infected. (Dr. Chandrika Ramadugu, University of California Riverside, 2016).
Thank you for supporting research to help save organic citrus. Your generous contribution to The Organic Center has helped to foster many of these experiments, including the direct funding of Dr. Rogers and Dr. Brlansky’s studies, the plantings of tolerant Sugar Belles, the identification and study of survivor trees, and the cooperation and partnerships with Dr. Roper and Dr. Ramadugu at UC Riverside. All of these efforts continue in part due to PCC’s continued support of The Organic Center.
Ben McLean III is the head of research for Uncle Matt’s Organic in Clermont, Florida. Founded in 1999, Uncle Matt’s Organic is the nation’s oldest organic orange juice brand. Together with his brother, Matt McLean, founder of Uncle Matt’s Organic, and their father Benny McLean Jr., the McLeans farm and manage more than 500 acres of organic citrus, peaches, vegetables and hay crops.