Spraying antibiotics on oranges is risky — and it appears it may not work, either

May 14, 2020 7:00 am

Florida oranges, the state’s signature crop, have recently battled citrus greening. Photo from Florida Citrus Commission

Remember the story of the old lady who swallowed a fly? She kept putting bigger and more dangerous animals down her gullet to fix the problem — first a spider to catch the fly, then a bird to catch the spider, then a cat to catch the bird and so on.

Something similar is going on in Florida’s citrus industry these days.

The coronavirus has prompted a surge in orange juice sales, reversing a long-term trend away from Florida’s official breakfast drink. But that’s a rare bit of good news for citrus growers.

You may have heard that they are battling a disease called “greening.” It’s spread by a bug — not a fly like the one the old lady swallowed, but an insect known as the Asian citrus psyllid. The psyllid feeds on stems and leaves, passing on the bacteria that carries the disease.

Greening attacks the tree’s vascular system, clogging it up and drastically reducing the transport of water and nutrients to the fruit, which turns out small and sour.

First identified in China in 1919, greening has spread to Africa, Asia and South America. So far there is no cure. The only treatment recommended by the U.S. Department of Agriculture is to cut down and haul away infected trees before the disease spreads throughout a grove.

The first case of greening in the U.S. was spotted in Miami-Dade County in 2005. Within the year, groves in twelve Florida counties had been hit. By 2014 greening had spread to every county with a citrus grove, as well as to groves in Louisiana, Georgia, South Carolina, Texas and California.

Before greening began ravaging their trees, Florida citrus growers produced 242 million boxes of oranges across 546,800 acres. Last year, they produced 74 million boxes across fewer than 400,000 acres. As you can imagine, the citrus growers are frantic to stem their losses.

One of the treatments they’re experimenting with involves spraying antibiotics on the trees to kill the bacteria. The antibiotics, streptomycin and oxytetracycline, are normally used to treat people suffering from such diseases as tuberculosis and syphilis.

Like swallowing spiders, birds and cats, spraying lots of antibiotics on the greening bacteria has a downside. Researchers with the U.S. Centers for Disease Control and Prevention concluded in 2017 that spraying streptomycin and oxytetracycline is tied to antibiotic resistance in bacteria that cause serious human health threats.

Nevertheless, in December 2018, the U.S. Environmental Protection Agency told Florida’s citrus growers they had “emergency” permission to spray antibiotics on their trees. The agency decided that the economic benefits of stopping the greening outweighed potential harm to the environment, people, and wildlife.

But what if you took that big risk and still didn’t solve the problem? What if you swallowed a spider and a bird and a cat and you still had your original fly problem plus all those other animals now running around inside you?

“There are real concerns about whether or not this works,” said Alexis Andiman, an attorney for Earthjustice, which has been battling the antibiotic spraying on behalf of farmworker groups fearful of the human health effects.

A University of Florida study released six months ago found that spraying oxytetracycline on citrus trees did absolutely nothing to halt greening.

“Researchers sprayed the leaves of infected orange trees with the oxytetracycline over a six-month period at concentrations recommended by the drug’s manufacturer but found no difference in the progression of the disease compared to trees that were sprayed with just water,” The New York Times reported in October.

The UF scientists had better luck with injecting the antibiotic directly into the tree trunk, but that approach also had drawbacks. Injection costs a lot more, they found, and also left three times as much antibiotic residue in the fruit.

Now even the citrus growers are no longer as keen on spraying. After more than a year of trying antibiotics, “some growers say they have had some success with it, and others say they haven’t,” Andrew Meadows of the Florida Citrus Mutual, a trade association with more than 3,000 grower members, said this week. “It’s tough to get a consensus on it…I don’t think it’s being used as much as we expected.”

One grower who supports continuing the spraying is Roy Petteway, chairman of the Peace River Valley Citrus Growers Association. He calls it “another tool in our toolbox.”

Other tools, he said, include changing from dry fertilizer to liquid and focusing more on the health of the roots than the fruit. He said that those steps, combined with the antibiotics spraying, have helped his trees produce up to 40 percent higher yields than four years ago.

The EPA’s emergency exemption was approved while Adam Putnam was Florida’s agriculture commissioner. I asked Putnam’s successor, Nikki Fried, if she’s going to support extending the exemption when it runs out. The answer: It’s up to the growers.

“As of now, we do not know if agricultural producers will request a petition to extend this product’s usage under an emergency exemption,” her press secretary, Max Flugrath, told me.

So we’ll see. And in the meantime, get ready to send in the dog, the goat, the cow and the horse. (Well, maybe not the horse.)

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Craig Pittman
Craig Pittman

Craig Pittman is a native Floridian. In 30 years at the Tampa Bay Times, he won numerous state and national awards for his environmental reporting. He is the author of six books. In 2020 the Florida Heritage Book Festival named him a Florida Literary Legend. Craig is co-host of the "Welcome to Florida" podcast. He lives in St. Petersburg with his wife and children.