Recent Views on Citrus Greening

From time to time, Richard Lyons’ Nursery has kept visitors to this website abreast of developments with regard to citrus greening disease. You probably know by now that, in spite of large expenditures of state and federal funds in support of research, no cure for the disease has yet been found. Various forecasts for the future of commercial citrus in Florida have been made, and none is particularly upbeat.

One of the more positive predictions came from Dr. Stephen Futch at the University of Florida citrus research and education center in Lake Alfred. He contends that there “will always be a citrus industry in Florida, but it will be different in the future than it is today. We will have to learn to live with the disease or come up with a solution; by creating an improved tree that will resist the disease.”

A considerably more dire forecast was voiced earlier this month. The source was Dr. Bob Shatters, a research molecular biologist with the USDA’s Agricultural Research Service (ARS) in Fort Pierce. In a July 13 speech in Clearwater, Shatters said that those involved in Florida’s citrus industry – despite knowing that citrus greening disease could appear in the state – were ill-prepared to deal with it once it materialized.

One factor that has inhibited a successful approach to treatment is that citrus greening has a long latency period, exceeding two years, before external symptoms appear on trees. The investigative process is further complicated because the bacterium cannot be cultured in the lab.

Fruit production on the average tree infected with citrus greening is only 40% of that of a healthy tree. That fact alone is enough to drive some growers out of business. To make matters worse, the cost of trying to maintain diseased trees has more than doubled. Shatters believes that 80-90% of Florida’s citrus is already, or is about to be, affected by the disease. His may even be a relatively optimistic view, since some people in the industry predict that 100% of citrus will ultimately be attacked.

Shatters warned that Florida’s citrus industry is at a “tipping point.” Although promising research is emerging, the clock is ticking. He urged that new findings need to be implemented in stages so that growers can hang on until even better strategies are developed. Ominously, he cited mathematical and epidemiological models that predict that the Florida citrus industry will no longer be commercially viable by 2019!

In the effort to combat citrus greening disease, the State of Florida has diverted $15 million from advertising into research, and the federal government has allocated $130 million to assist Florida and California. Shatters reported that thermal therapy is one way to prolong the life of a diseased citrus tree. Large canopies are placed over trees, and hot water or steam is then injected for a minute or less to heat up the trees. The bacterium is sufficiently heat-sensitive to die from the thermal therapy, and the treated trees experience at least two years of improved growing conditions.

Other techniques have also been employed to slow down the advance of citrus greening disease: Dogs trained to detect the disease early, improved root stocks, improved spraying technologies for killing the insect which spreads the disease, and enhanced nutritional programs for the trees. Finally, bacteriacides used elsewhere on apples and pears have been granted emergency registration in Florida for use on citrus, and early results from application in the greenhouse and in the field have been encouraging.

Shatters, in apparent agreement with Futch, concluded by stating that new varieties of citrus will provide the key to overcoming citrus greening disease. But the sense of urgency is acute; if citrus production in Florida drops below the level needed to sustain juice production, processing plants will close.

Richard Lyons’ Nursery has for some time been recommending against growing citrus in southern Florida, and nothing gleaned from these recently-reported developments changes that advice. Aside from citrus greening itself, Lyons is concerned about the viability of currently-popular root stocks. Most citrus grown upstate is grafted onto Swingle root stock, which is well-suited to acid soils. But fruit grown on Swingle root stock in southern Florida, where soils are alkaline, tends to be pithy and unsweet. He suggests that homeowners interested in cultivating citrus confine their efforts to Key Lime, which can be grown easily from seed and need not be grafted.

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