2003
NEWS ARCHIVE
Invasive
Weed Held In Check: Saltwater Helps Control Giant Salvinia
July 23, 2003
CAMERON -
"We sprayed it, we dried it, we burned it and we salt watered
it," Ben Welch said as he stood next to his airboat in the
Cameron Creole marsh near here.
The "it"
Welsh referred to is Salvinia molesta or giant salvinia - an invasive
weed that forms dense mats, which sometimes are several feet thick.
The weed was first identified in Cameron Parish in 2001. The fast-growing
aquatic plant can choke a waterway and kill plants and animals
underneath its thick covering. It was first discovered in Louisiana
at Toledo Bend in1998 by a biologist with the Sabine River Authority.
The weed can also clog irrigation systems and even compete with
rice crops if it's introduced into rice fields. Native to South
America, the plant has been a major problem for Brazil's rice
industry and poses a threat to Louisiana farmers.
Welsh, owner
of Welch's Airboat Service, has a contract with the Cameron Parish
Police Jury and the Cameron Parish Drainage Board to control giant
salvinia in 4,000 acres of the marsh known as the Henry-Davis
property. The infested region is blocked off from other areas
by high levees, roads and ridges.
When it was
first identified in Cameron Parish, giant salvinia was 4-5 feet
thick against bridges, and observers identified an area 5-6 miles
long and as wide as 2 miles on the Cameron Drainage Canal.
Since then,
Dearl Sanders, LSU AgCenter researcher, and Kevin Savoie, Louisiana
Sea Grant Extension Fisheries Agent, have been working with the
local agencies and Welch to control the weed.
In the hope
of finding a less-expensive alternative to chemical control, the
trio tried saltwater this past spring. The Henry-Davis property
was pumped nearly dry and flushed with saltwater from the Intracoastal
Waterway. "Saltwater did more good than anything else,"
Savoie said. The giant salvinia hasn't reappeared in areas of
the marsh where saltwater was introduced, officials said.
On the other
hand, in areas where levees held back the saltwater, giant salvinia
presents a never-ending battle being fought with chemicals and
other management tools.
Sanders, who
said the Cameron Parish infestation is the only one he knows that's
close to saltwater, is recommending the area be pumped dry and
flushed with saltwater yearly for about three years. "Where
saltwater can get, we just annihilated it," Welch said.
In other spots,
Welch still fights the weed with frequent herbicide applications.
One area was completely covered in May, but after spraying, it
was mostly clear in mid-July, he said. All that remain are "little
pockets." "It's like hide and seek," Welch said.
"It's not there one day, but it's there later."
Since May
1999, many have been looking for the best method to control giant
salvinia. They found that a herbicide called Reward, which is
available for use in the state, is the best means of controlling
the weed. One drawback, however, is expense. Reward costs about
$80 per acre for the chemical, and the application cost adds even
more to the expense. In Cameron Parish, the Louisiana Department
of Wildlife and Fisheries has supplied the Reward, and the local
agencies have paid for the application.
One aspect
of marsh management is controlled burning, Savoie said. Landowners
periodically will burn off the dead, dry grasses on dry ground
that emerges during periods of low water. It was during a burn
that Welch discovered fire is not a friend of giant salvinia.
When his crew burned some dry cover, the heat "baked"
the salvinia, Welch said. That salvinia didn't come back.
"We have
the benefit of a contractor who knows marsh management,"
Savoie said about Welch.
The Henry-Davis
property is used for duck hunting and to graze cattle, Savoie
said. But when open water is covered with giant salvinia, the
ducks can't land. And even if they did, they'd have nothing to
eat. Since the salvinia control program started, wigeongrass and
other grasses that provide food for waterfowl and wildlife are
coming back. "We are putting the area back into productivity,"
Savoie said.
Contacts:
Kevin Savoie at (337) 775-5516 or ksavoie@agcenter.lsu.edu.
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