The State of Citrus Greening
Ben McLean III, Uncle Matt’s brother, leads the company’s research department alongside Uncle Matt’s dad Benny. Their primary focus over the last decade and a half: Citrus Greening Disease. It’s also known as Huanglongbing (HLB), or yellow dragon disease.
While citrus greening, or “greening” as it’s referred to, is a problem worldwide, it is especially dominant in the state of Florida. It’s taken an extreme toll on the viability of the majority of citrus groves throughout the state over the last decade.
Greening is a bacterial disease that infects citrus trees causing the fruit to grow smaller, taste bitter, not fully mature, and ultimately drop off the tree early and rot. This is because the disease attacks the tree’s phloem (a tree’s main artery) which makes it very difficult for the tree to absorb nutrients. As the tree becomes more malnourished, the fruit produced lacks the bright, vibrant colors we associate with citrus – hence the name greening.
We chatted with Ben to find out about the background, ongoing research and future outlook on citrus greening disease in Florida. Right now, there’s no cure, but Ben says he’s hopeful that they are on the right track! Watch the video below or read the Q&A to learn more.
Q. Where did citrus greening originate and how did it get to Florida?
A. Citrus greening originated in China which is believed to be the birthplace of citrus. Greening was first reported over 100 years ago in China and is believed to have arrived in the United States in 2005-2006. It was reported in a South Florida commercial nursery and is believed to have arrived through contaminated vegetative material. The disease grafted into the trees and the disease spread from there.
Q. Why is citrus greening so pervasive within the industry, and why has it been such a struggle to find a cure?
A. Unfortunately, it’s so pervasive because the vector (carrier), which is the insect the Asian Citrus Psyllid, arrived in the U.S. a few years before the infected plant material arrived. The Asian Citrus Psyllid is effective at feeding on the leaves and phloem of the tree. This is called the vascular system of the tree. From there it picks up the pathogenic bacteria which is actually inside the infected plant material. The Asian Citrus Psyllid carries that pathogenic bacteria in its gut and flies around through the state – feeding and spreading the disease. Because we have many small trees in people’s yard settings, large commercial plantings, escape trees out in the woods… the Asian Citrus Psyllid found many opportunities to feed, spread and multiply throughout the state. Within about five years the disease became widespread from South Florida to North Florida.
Q. Why is greening so hard to control?
A. The Asian Citrus Psyllid is widespread, and we don’t have the ability to eradicate it because Florida is so diverse in its plantings. There’s so much plant material scattered throughout the entire state. It makes it very difficult not only to control the vector but then once the vector gets inside the plant it’s very difficult to control because it’s actually a circulatory disease within the plant.
It’s difficult (for researchers) to get inside the vascular system of the plant – the phloem and also the xylem – to put in some type of a material that would control this bacterial pathogen, inhibit its growth or even outright kill it. It’s almost impossible to break into the phloem of the plant. For us to get any type of material into the phloem…that’s very difficult. They have to go in through the leaf, get into the phloem, then circulate throughout the plant. This has presented a great challenge to us to actually manage this disease.
Q. What organic practices and tools are you using to help in combating citrus greening disease?
A. We actually have some really great tools in organic citrus production to combat the citrus greening disease. One of the best and most important tools we have is improved genetics. We have good breeding programs (through partnerships) with the University of Florida and the USDA. They’ve come out with tolerant root stalks and tolerant scion varieties like these Valencias which are showing a lot more resistance to the disease. Those can be used by organic growers because they came from a conventional breeding system. They’re not genetically engineered or considered GMOs. As an organic citrus grower, I’ve got the best tool out there which is improved genetics.
Now to control the vector, the Asian Citrus Psyllid, I have two really good sets of tools. I have access to botanical oil such as neem oil and clove oil which actually give us good control of the Asian Citrus Psyllid without harming our beneficial populations. Secondly, we have access to beneficial wasps. Tamarixia wasps are grown at the University of Florida. My dad receives these packages weekly and releases this biological control out into our grove. We’ve actually found that by combining the botanical oil with these beneficial wasps releases that we’ve been able to keep these populations down very low in our organic grove.
Q. What’s on the horizon for citrus greening and are you hopeful there will be a cure one day?
A. We are hopeful and feel we are getting close to a cure right now. With our improved tolerant genetics, our biological control program, and an enhanced nutritional program – with a robust application of micronutrients particularly zinc, manganese and boron, that these tools together give us optimism that we can profitably produce citrus organically in the state of Florida.