To combat citrus greening, farmers are spraying medically important antibiotics on their trees

Citrus greening first appeared in China nearly a century ago. In the U.S., the tiny winged Asian citrus psyllid arrived years before the harmful bacteria. The pest was first confirmed in Florida in 1998, and Huanglongbing followed in summer of 2005. The psyllid proved a powerful carrier, spreading the bacteria from tree to tree as it fed on citrus leaves and steams. Within a few months, the bacteria had spread to four counties. Two years later, it had spread to 30. By 2015, it had hit every citrus-producing county in the state, and today an estimated 90 percent of the state’s citrus trees are infected. Florida produces more than two thirds of the nation’s citrus and more than 90 percent of the orange juice. 

It wasn’t long before Florida growers were desperate to try anything to stop citrus greening disease. By 2016, a survey found that producers were self-reporting an average yield loss of 40 percent as a result of the disease. That year, EPA began allowing Florida growers to spray so-called “emergency applications” of two antibiotics—streptomycin and oxytetracycline—on their citrus crops. Both are considered medically important to humans: They’re used to treat urinary tract infections, syphilis, and tuberculosis. 

The decision sparked concern among public health advocates. “This is almost a panic response,” said Steven Roach, senior analyst for Keep Antibiotics Working, in an interview last year. The agency was proposing to allow as much as 650,000 pounds of streptomycin to be sprayed on crops each year. That’s more than 10 times the amount used to treat human diseases. The concern was that the widespread use of antibiotics on crops would select for antibiotic-resistant bacteria, which would then spread throughout the ecosystem. 

Antibiotic-resistant infections are expected to claim 10 million human lives by the year 2050, and critics worry the spread of so-called “superbugs” will be aided by the extensive use of antibiotics in agriculture. Limited testing of antibiotics on citrus has indicated that spraying would do little harm; however, public health advocates worry about the potential consequences of spraying at a large scale. 

Still, in December 2018, EPA approved the use of oxytetracycline as a routine treatment on citrus groves, meaning the antibiotic could be used without the agency having to issue its emergency exemptions. The New York Times reported that, in doing so, the agency largely ignored objections from the Centers for Disease Control and Prevention and the Food and Drug Administration. A similar approval for streptomycin has not yet materialized; the agency quietly acknowledged in January that it had approved emergency use of streptomycin in Florida and California in 2019. 

It’s up to the Food and Drug Administration to ensure the safety of the food supply; EPA’s mandate is protecting the environment. That’s partially why critics argue that EPA is ill-equipped to evaluate the potential impact of antibiotics used on farmland. “When they do pesticide registration, EPA obviously has no reason to look at things like antibiotic resistance, because you’re looking at other types of environmental harm—other types of pesticides don’t cause antibiotic resistance,” says Emily Knobbe, EPA Policy Specialist at the Center for Biological Diversity. “So why would you have to look at things like that? EPA doesn’t have the experience to conduct those types of studies.” 

For growers like Meador, spraying with antibiotics means the cost of doing business has risen sharply. He remembers spending $1,000 per acre on production costs less than two decades ago. Now he spends $3,000. And the rising bills have been accompanied by a slump in yield. Production on his land has diminished by half, if not more, Meador says.

That said, Meador says the bactericides have made an impact in the long run. “If you grow vegetables, you can … get a very quick response—you can see within a day or two that what you’ve done is accomplishing something. In tree crops things are subtle changes, kind of like guiding a big ship. It takes a while to change directions,” he says. The first year, he noticed that the leaves on his trees looked healthier, and they were dark green instead of mottled, but the fruit was still falling before it had ripened. During the second year, he still saw some fruits fall prematurely, but found that the impact of the disease was substantially diminished, especially compared to growers who were not using antibiotics. 

But while Meador has been pleased with the results, a study conducted last year at the University of Florida was much less conclusive. Researchers examined the impact of oxytetracycline sprayed on citrus groves over the course of six months and found that the antibiotic did little to suppress bacterial populations in the trees tested. The waxy coating on the leaves may have prevented the trees from absorbing the antibiotic. A representative from the University of Florida said similar tests have not been conducted for streptomycin. There are a few different possible explanations for the difference between Meador’s experience and the results in the lab—Meador has used the bactericides for much longer than the study lasted, and he has used both streptomycin and oxytetracycline. 

The researchers in Florida did find that injecting the antibiotics directly into tree trunks, rather than spraying them onto leaves, may hold promise. “One challenge is, the oxytetracycline needs to get into the tree tissues where the bacterial colonies are,” said Dr. Michael Rogers in a press release. By injecting the drugs directly into the trunks, scientists were better able to target the bacteria. There’s just one problem:  Injections are not currently EPA-approved. Also, The New York Times reported, the fruit from trees that had been injected with oxytetracycline had high levels of antibiotic residue.

Other anecdotal research suggests growers have tried using antibiotics and later abandoned them. An informal survey of 38 growers conducted by Mongi Zekri of the University of Florida found that while most—80 percent—had tried using antibiotics at some point, more than half had since stopped. An additional 20 percent of growers reported that they continued to use antibiotics on their groves, but not for citrus greening. 

It may be that, for some, bactericides are just too expensive to keep using if they don’t show obvious results. Meador has had to adjust his budget in order to keep using them, cutting down on the amount of compost he adds to his groves in order to save money. 

In the future, Meador says he hopes scientists will find a way to breed trees that are resistant to Huanglongbing. Other management approaches, like building protective covers over orange groves, are cost-prohibitive for now. “Nobody’s going to be able to afford orange juice if you have to grow orange trees under cover,” he says. “It would just simply put us out of business. 

For now, Meador is convinced bactericides will continue to play a role in citrus greening management for the foreseeable future, despite concerns about effectiveness and potential externalities. “Without them, until plant breeding or other technology catches up, I don’t think the industry will thrive. It’s an important tool in the toolbox for those who want to stay in the industry.”