At the May 10 South Florida Water Management District Governing Board meeting, member Ben Butler said he’s heard “numerous concerns” about the district’s use of herbicides.

Butler, manager of the family-owned dairy farm Butler Oaks Farm north of Lake Okeechobee, insisted that as long as the chemicals are being used correctly, “they are tools we absolutely do not need taken away from us,” adding that in some instances “there is not another alternative.”

But there’s definitely reason for concern.

According to the district’s 2024 South Florida Environmental Report: “Herbicides approved for aquatic use or in terrestrial natural areas are a vital component of most control programs and are used extensively for invasive plant management in South Florida.”

To be fair, the district uses an “integrated pest management” or IPM approach that includes “prescribed burns, hydrologic restoration, physical (aka mechanical) removal, selective herbicide application and other natural predators (biocontrol) like Lygodium moths,” according to a statement from district spokesman Randy Smith, who adds, “The use of the IPM approach provides better results than any one method could achieve on its own.”

Still, the district uses over 20 types of herbicides to control 84 species of invasive plants, in what Smith called “one of the nation’s largest invasive plant management programs.”

The district targets aquatic plants such as hydrilla, water hyacinth and tropical American watergrass in the Kissimmee River basin, Lake Okeechobee and SFWMD’s stormwater treatment areas and canal system also uses herbicides on numerous terrestrial plants such as Old World climbing fern (a.k.a. Lygodium), melaleuca and Brazilian pepper.

Of those 20 types of herbicides, glyphosate is likely the best known — and perhaps the most controversial.

Glyphosate, the active ingredient in Roundup and Rodeo herbicide products, is the world’s most widely used herbicide. It also poses potential health risks to humans and animals. It’s classified as “probably carcinogenic to humans” by the International Agency for Research on Cancer, particularly non-Hodgkin lymphoma.

A district-sponsored web page titled “Plants Behaving Badly: Lygodium” recommends controlling the plant also known as Old World climbing fern in dry areas with herbicides “like Brush-B-Gone (triclopyr amine 8%), Brush Killer (triclopyr amine 8.8%), ‘Ready-to-use’ Roundup (glyphosate .96%), Roundup Pro (glyphosate 41%) and Roundup Super Concentrate (glyphosate 41%).”

As a warning, the district notes that “these herbicides should only be used in dry areas. They may not be applied directly to water.”

To control “floating aquatic plants or plants growing along a shoreline (where spray will contact the water),” the district says the “herbicide Rodeo (glyphosate 53.8%) can be applied directly to the plant when it is growing over water.”

Rodeo is considered safer for aquatic environments because it does not contain the surfactant, which helps herbicides stick to and penetrate leaves, found in Roundup.

Safer, maybe, but how safe?

‘Chronic’ in manatees

The study “Chronic Exposure to Glyphosate in Florida Manatee” published in the July 2021 edition of Environmental International showed “a chronic presence of glyphosate in Florida water bodies with higher concentration and exposure to Florida manatees in South Florida.”

The study noted that glyphosate can “be sprayed directly into water bodies using specific formulations to control aquatic weeds,” reach surface water bodies through runoff and up to 58% of its application can be blown away by wind.

The study focused on glyphosate levels in manatees, finding the herbicide in the plasma of 55.8% of the sea cows sampled and that the concentration has increased from 2009 to 2019.

Researchers also found that the Florida Fish and Wildlife Conservation Commission sprayed up to 10,000 kilograms (about 22,050 pounds) of glyphosate per year in Lake Okeechobee and that Army Corps of Engineers’ Lake O discharges sent high concentrations of the herbicide to the Caloosahatchee and St. Lucie rivers.

Now you might think: Hmm, herbicide in the water ought to help kill the blue-green algae blooms that plague the Caloosahatchee and St. Lucie rivers during Lake O discharges. But …

Glyphosate is a phosphonic acid and can be metabolized by microorganisms in soil and water, releasing phosphate (a form of phosphorus) as it breaks down.

A 2019 study titled “Glyphosate use linked to phosphorus pollution in water bodies” reports what people living along the St. Lucie and Caloosahatchee rivers and the Indian River Lagoon have learned the hard way: that excessive phosphorus in the water can “induce excessive growth of plants and algae (the latter can sometimes be toxic). This overgrowth can result in oxygen depletion of the water body. Larger life forms, such as fish, can suffocate to death.”

Glyphosate and the sugar industry

Back to the study on glyphosate and manatees: It also found that glyphosate “has been used intensively in sugarcane plantations in Southern Florida, located in the Everglades Agricultural Area, south of Lake Okeechobee since 1980,” not only for weed control but “as a ripener to increase the total recoverable sugar. … Glyphosate is normally applied 2–5 weeks before harvest, and harvest spans from October through March, making glyphosate intensively applied during the entire period.”

Measuring devices researchers placed in a stormwater treatment area (STA 1 West) south of Lake O and in the St. Lucie River “had the maximum accumulation of glyphosate per day during the sugarcane harvest period. Both sites are in direct proximity to sugarcane plantations in the Everglades Agricultural Area, in counties with the highest production of sugarcane in the United States.”

Remember: As glyphosate breaks down, it releases phosphorus — the very chemical the stormwater treatment areas were built to remove from water flowing into Everglades National Park.

On the bright side: Manatees sampled along the Georgia Coast, north of the mouth of the St. Johns River near Jacksonville “showed a significant decrease in glyphosate concentration from 2017 to 2019.”

Why? The study’s authors think it could be the fact that the Florida Fish and Wildlife Conservation Commission reduced applications of glyphosate in the St. Johns River from 446 pounds in 2017 to 11 pounds in 2018 and none in 2019.

Consider the alternatives

So reducing, and even eliminating, glyphosate use is possible. Which brings us back to the other controls used in the South Florida Water Management District’s “integrated pest management.”

The district says it works “to optimize each of our pest management methods and reduce the amount of herbicides used to manage invasive species at the lowest feasible level” by:

• Using the latest technologies to improve efficiencies
• Increasing weed barriers across canals to prevent the spread of invasive plants
• Mowing more often and in more areas
• Chemically spot-treating invasive plants
• Using mechanical harvesting at weed barriers
• Introducing sterile grass carp to reduce invasive vegetation in canals, “a low-cost, long-term herbicide-free way of controlling nuisance plants”
• Searching to find and produce more natural predators including insects that eat invasive plants
• Requiring local canal operators to take proactive measures to reduce the amount of vegetation entering district canals

You can help, too. Invasive plants and animals are often introduced into the environment by people. So:

• Never dump unwanted pets or plants.
• Remove invasive plants from your yard and consider Florida-friendly landscaping.
• Understand local laws and regulations for owning plants and animals that may impact the environment.
• If you come across an invasive species, call 888-Ive-Got1 or report it using the app called IveGot1.

At that same district board meeting in May, member Charlette Roman, a retired Army colonel from Marco Island, followed up Butler’s comments by saying the district “did set a goal for reducing herbicide use.

“Maybe it’s time for an update to see how we’re doing,” she said.

We’d all like to see that.