Invasive
Weed Held In Check: Saltwater Helps Control Giant Salvinia
Posted:
7/23/03
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
Download:
invasive_weed.pdf
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