WEST PALM BEACH — The South Florida Water District is working to reduce the use of herbicides to control exotic plants, SFWMD Vegetation Management System Section Administrator Francois Laroche explained at the Water Resources Accountability and Collaboration (WRAC) May 28 online meeting.

“We are aiming for about 20 percent reduction of herbicide use over the next five years,” he said.

SFWMD manages 2,600 miles of canals, 430,000 acres of lakes and water bodies and 78,000 acres of stormwater treatment areas (STAs) and flow equalization basins (FEBs).

He said herbicide compounds interfere with plant-specific metabolism functions, disrupting photosynthesis, amino acid synthesis and plant growth hormone production. Systemic herbicides are absorbed through the roots and kill the plants. With contact herbicides, when they touch the leaves, it will kill the plant.

He said SFWMD only uses herbicides that have been EPA approved for use in sensitive environments. These herbicides have low toxicity and a short half life, Mr. Laroche said. SFWMD has a Federal Clean Water Act permit for their herbicide use.

He said maintenance control is the ultimate goal. In the first phase, they will target the canals and levees to find ways to control exotics while at the same time reducing herbicide use.

They are looking at different herbicides and different methods of treatment in order to use less active ingredients to control the undesirable plants.

Mr. Laroche said they are evaluating different machines to apply herbicide more efficiently to the target plants without endangering the native vegetation.

Aquatic plant harvesting is another option to reduce herbicide use, he continued. A WEEDO machine was used to remove floating plants in the Monkey Box area on Lake Okeechobee in one demonstration project. The project area was about 4 miles offshore, he continued, so the use of small barges to transport the material increased the cost. These machines are more efficient closer to shore, he said.

They are also experimenting with an innovative machine that has a basket to hold the vegetation until it can be hauled to the shore. Another innovation is a GPS tracking system to make the harvester pattern more efficient.

He said they are working with the University of Florida Institute of Food and Agriculture Services (UF/IFAS) to research ways to use harvested aquatic plants as livestock feed.

Mr. Laroche said they are also working on ways to encourage property owners to control plants in canals on private lands before they flow into SFWMD canals.

He said they are using weed barriers in SFWMD canals to catch and collect floating weeds. “Rather than use herbicides to control these plants, we are looking at using more mechanical harvesting,” he explained.

Increasing flat mowing, slant mowing and weed-eating on the levees can reduce the need for herbicide use, he continued. Mowing more often may suppress the nonnative plants.

“We used to use helicopters to broadcast herbicide on our levees,” Mr. Larcoche explained. “As we are getting control on those levees, we stopped the use of helicopters.” He said a sprayer can be used to control the tall grasses and broad leaf plants that interfere with the levees. With new technology, a helicopter can be used to spray individual trees in remote areas.

“We need to improve our program oversight with more training for our staff and contractors,” said Mr. Laroche. New technology will also mean greater oversight of the herbicide applicators. A GPS system can monitor where the spray boats have been as well as how often and how long the applicator presses the spray gun trigger in the varying locations. This will allow SFWMD staff to determine how much herbicide was used as well as when and where it was used.

In the past 10 years, SFWMD has reduced herbicide us by about 60 percent, he said. They plan to continue to evaluate new approaches to continue to reduce herbicide use.