Invasive Hydrilla

Water managers struggle with invasive hydrilla

After a Gulf Coast aquarium dealer had the plant shipped from Sri Lanka in the early 1950s, the stringy nuisance has cost government agencies countless millions. Hydrilla grows up to two inches a day, clogging lakes, rivers and canals that flow to the Melbourne-Tillman (C-1) canal in Palm Bay. That, in turn, raises flood risks.

So Florida water managers spray upward of $15 million worth of herbicides annually to keep the invasive plant in check on public lands — with uncertain environmental consequences.

The Melbourne-Tillman Water Control District uses a slow-release herbicide called fluridone (brand name Sonar), spending about $120,000 annually to control hydrilla in 163 miles of canals in the 100 square-mile district. They plan to apply the herbicide again in the next few weeks.

But as government gears up to spend millions to dredge muck from Turkey Creek and the Indian River Lagoon (IRL), one longtime, avid river advocate is raising concerns that the herbicide might be killing seagrass at the mouth of the creek and fouling the lagoon with rotted, dead hydrilla and other plants.

"Why are we creating muck upstream from the Indian River Lagoon and letting it flow down into the IRL, while we spend millions of dollars to remove the muck from the IRL?" said John Mongioi, a longtime river advocate and Palm Bay resident.

Nobody knows whether fluridone is killing seagrass. Experts doubt it. But some scientists say the herbicide might be worth testing for in waters near seagrass. And recent concerns about the lagoon could lead to more environmentally friendly ways of handling hydrilla. Water managers want to limit how much dead, rotted hydrilla builds up as muck along canal bottoms. Plant ecologists say herbicide is the most practical, affordable way to control hydrilla and other nuisance water plants. But this die-hard plant defies simple solutions.

"It's so complex, all the facets of trying to control this stuff," said Dan Anderson, manager of the Melbourne-Tillman district. "There's just no quick fix."

Mongioi has been pushing the district to find a better way. He was chairman of Friends of Turkey Creek. The now-defunct volunteer group for a decade represented more than 200 homeowners along the creek and pushed for dredging the creek and other improvements to the lagoon.

Melbourne-Tillman district has used fluridone for years. The herbicide was first registered with the U.S. Environmental Protection Agency in 1986.

Hydrilla haven

Helping the lagoon unintentionally set the stage for hydrilla to thrive.

The invasive plant has grown worse in Melbourne-Tillman's canals since 2011, when a new dam structure went in as part of efforts to hold back nutrient-rich fresh water from flowing to the lagoon. That created a hydrilla haven.

"Now that we're holding the water back, it's like Miracle-Gro," Anderson said.

District officials — bolstered by scientists who study fluridone — say the herbicide is safe. The district must remove hydrilla to prevent the plant from clogging up canals and water control structures that provide flood control for some 80,000 people, district officials say. The district spends $1,100 an acre to treat hydrilla with the herbicide, Anderson said, so they are very careful not to over-use it.

"It's essentially nontoxic to wildlife — shrimp and invertebrates — because it inhibits the production of chlorophyll, and animals don't do chlorophyll," said William Haller, acting director of University of Florida's Center for Aquatic and Invasive Plants. He conducted some of the early tests on fluridone.

"It doesn't kill many other plants other than hydrilla," he added. "A lot of other native plants will survive the treatments."

Using the herbicide early in the spring minimizes muck, because it kills hydrilla while the plant is very small, he said.

Haller doubts any impacts to downstream seagrass, because the herbicide would be so diluted by the time it reaches seagrass.

Nonetheless, Anderson said the Melbourne-Tillman district is in discussions with state environmental officials about conducting water tests to see whether the herbicide remains at levels that might harm seagrass.

Fluridone may be worth testing for, says John Windsor, a professor of marine and environmental sciences at Florida Institute of Technology. But finding herbicide near seagrass is a far-cry from proving it's a problem.

"I understand the concern ... herbicide in a canal that runs to a place where seagrasses are dying," Windsor said. "It seems like it's a good thing to consider."

But he says tests could be expensive and yield no answers.

"It's something that people should be concerned about," he added. "But we have such a long list of concerns. If we had an infinite amount of time and an infinite amount of money, we should be looking at all of it."

Meanwhile, the Melbourne-Tillman district hopes to team with Brevard County to harvest some hydrilla and other excess water weeds mechanically. Brevard plans to buy a small mechanical harvester with $118,000 state grant the county received last year.

But Anderson said his district would need a much larger machine to make a significant dent in the district's hydrilla onslaught. Melbourne-Tillman hopes to buy its own larger mechanical harvester, which Anderson says would run about $250,000.

Melbourne-Tillman also hopes to partner more with the St. Johns River Water Management District to battle back hydrilla.

But Anderson says it would be too costly to harvest hydrilla throughout the entire 100 square-mile district.

Mechanical harvest is often impractical, especially in remote areas, says Gary Nichols, supervisor of the St. Johns River Water Management District's invasive plant program.

"Then you have to have an area to go dump it," Nichols said.

Bass like hydrilla for hiding places, but the plant has few natural enemies.

"A lot of waterfowl eat it," Nichols said. "Coots can decimate hydrilla."

Biologists once considered introducing manatees to eat back hydrilla in certain Florida springs, but they found sea cows wouldn't make enough of a dent in the plant to make it worthwile.

Source: Florida Today

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