UF researchers seek bugs to battle aquatic weed plaguing Central, South Florida

April 21, 2008

GAINESVILLE, Fla. — Years of hydrilla control efforts have paid off for some Florida communities — unfortunately, their success has benefited a more troublesome aquatic weed, a University of Florida expert says.

For the past decade Hygrophila polysperma — a southern Asian plant known as “hygrophila” for short — has been taking over the ecological niche left when hydrilla was eradicated from waterways, said Jim Cuda, a UF associate professor of entomology. It’s now a significant problem in South and Central Florida.

Like hydrilla, hygrophila (“high-GRAW-fill-uh”) was sold as an aquarium plant, got into Florida waters decades ago and survived. But the similarities end there.

Hydrilla is strictly a water weed, and can be controlled with herbicides, hungry grass carp or mechanical harvesting. Hygrophila can grow fully submerged or up on river banks. Herbicides aren’t very effective, grass carp don’t like it, and mechanical harvesting breaks its stems into tiny pieces capable of spawning new plants.

Given that scenario, Cuda and colleagues with UF’s Institute of Food and Agricultural Sciences are looking for natural enemies that attack the plant on its home turf in India.

‘There aren’t any good, cost-effective management options for hygrophila,” Cuda said. “That’s why there’s interest in biological control.”

Last fall, Cuda and entomology graduate student Abhishek Mukherjee made a collecting trip to several Indian states, described in an article published in the spring issue of Aquatics, journal of the Florida Aquatic Plant Management Society.

The researchers found evidence of at least one insect Mukherjee hopes to capture on a return trip this summer. They also collected samples of wild hygrophila that are being genetically analyzed to determine if they’re identical to plants found in Florida.

If so, that would mean insects and diseases found in the same parts of India would be likely to attack the Florida hygrophila. If not, the researchers may keep trying to pinpoint the original home of Florida hygrophila and seek enemies there.

The UF team — which includes Cuda, Mukherjee and Bill Overholt, also a UF associate professor of entomology — recently discovered that the larvae of a native moth species will feed on hygrophila.

The moth has no value as a biological control agent because it isn’t host-specific — the larvae attack more than 60 plants — and is unlikely to put a dent in hygrophila populations. But it can be a great research tool, enabling researchers to find out if hygrophila can survive defoliation, Cuda said.

Hygrophila closely resembles native alligatorweed, he said. Residents who think they’ve found a patch should not try to destroy it, but instead contact their county extension office, which can be found at www.solutionsforyourlife.com.

In the United States, hygrophila is currently growing wild only in Florida and Texas. It’s been officially confirmed in 10 Florida counties, though Cuda suspects it’s present in at least 20. Previous research indicates the weed can survive cold climates, and could potentially spread as far as hydrilla did — from Delaware to Florida, all along the Gulf Coast, and north to Washington state.

In Texas, hygrophila has already become established in two lakes and a river system, said Marcos De Jesus, a state fisheries biologist with the Texas Parks and Wildlife Department. But right now, the population is small and other invasive aquatic weeds take priority.

“The money goes into chemical control or mechanical removal of these other species and hygrophila hasn’t spread enough to warrant a lot of attention,” he said.