Pesky fern has
molested pond in Hilo

Experts believe salty sea water
has helped keep it under control

By Rod Thompson

HILO >> The same waterweed that clogged Lake Wilson in Wahiawa has been found twice in Hilo's Wailoa Pond.

Both times, including last week, crews from the state Aquatic Resources Division killed it before it multiplied, said the agency's Hilo biologist Robert Nishimoto.

The offending plant, called Salvinia molesta, is a fern that does not look much like a fern. It is only a few inches across and can form giant interlocking mats.

It was discovered in a single patch in the Hilo pond last fall by an aquaculture farmer, Nishimoto said. Officials killed it using Aquamaster, the new brand name for the glyphostate-based herbicide formerly known as Rodeo, he said.

Since individual plants are small, they can stay hidden in California grass, a much larger weed that also affects Wailoa Pond, Nishimoto said.

Another outbreak was poisoned last week, he said.

"It's something you really can't get totally rid of. We got the marching order to be very vigilant," he said.

A U.S. Geological Survey Web site shows that salvinia is a pest in several Southern states, yet it also is or has been deliberately cultivated in 16 states, including Hawaii. It is apparently grown commercially as a decorative plant.

A 1999 survey in California found it for sale in commercial nurseries in 48 cities there, the Geological Survey site says.

Federal law has made it illegal to transport it across state lines for many years, but transporting it within a state depends on each state's laws, the Web site says.

Nishimoto keeps a small fishbowl filled with the little plants in the state Department of Land & Natural Resources office in Hilo for anyone who wants to check them out.

Unlike landlocked Lake Wilson, Hilo's Wailoa Pond is connected to Hilo Bay. Since tides carry salty sea water into the pond, that may help control the weed there, Nishimoto said.

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