Lake Bistineau

Freshwater

What is giant salvinia?
Giant salvinia is a free-floating aquatic fern native to Brazil. It was brought into the U.S. by the aquarium and water garden industry.
How fast does giant salvinia grow?
This plant has the potential to double in biomass every 3-5 days. On Lake Bistineau, the plant is growing at a tremendous rate, doubling every week to 10 days during the prime growing season.
When was giant salvinia first discovered in Lake Bistineau?
The invasive aquatic plant giant salvinia was discovered on Lake Bistineau in February of 2006.
How did giant salvinia get into Lake Bistineau?
Giant salvinia was likely transported to Lake Bistineau on one or more boat trailers sometime during the 2005 drawdown.
Is this the only lake with this problem?
No. Giant salvinia has been found in nearly every public water body in northwest Louisiana and continues to spread to other areas of the state.
Why can’t you simply spray it and kill all of it?
Giant salvinia is very difficult to control with foliar herbicide applications because the leaves have specialized hairs that are very efficient at keeping water off the leaf making it very difficult for herbicides to be absorbed by the plant.
Why don’t you spray it from the air?
LDWF has a contract for aerial herbicide applications but there is a fairly long lead-time in letting the contract and arranging for an application to be made. At times, large mats of giant salvinia can be found in open water areas of the lake that would be suitable for aerial applications. However, when the wind changes the salvinia is blown to other areas of the lake where the cypress canopy or adjacent inhabited shorelines do not allow for aerial applications.
Why don’t you put grass carp in the lake and let them eat it all of it?
Giant salvinia is not considered a preferred diet choice for grass carp.
Did last year’s drawdown do any good? The lake is just as bad now as it was last summer in front of my house.
There were approximately 4,500 acres of giant salvinia on Lake Bistineau prior to the July 15, 2008, start of the drawdown. In conjunction with ongoing herbicide applications, dewatering the lake and allowing the giant salvinia to dry and desiccate had reduced the salvinia to approximately 850 acres in mid-March of 2009. This reduction in acreage was short-lived as heavy rains and a resulting rise in lake level beginning in May 2009, flushed large quantities of salvinia down to the lower end of the lake. With warming temperatures the salvinia began growing very prolifically, causing problems in these areas including boating and fishing access and aesthetics issues for shoreline property owners.
Why don’t you just drain the lake and leave it down for a couple of years?
With the drawdown structure that is currently in place, the maximum drawdown capability of Lake Bistineau is seven feet below normal pool stage. A drawdown to this level reduces the surface acreage at pool stage by approximately half. Giant salvinia continues to grow in the remaining water, much of which is extremely difficult to access by boat for herbicide applications. Lake Bistineau also has a very large watershed and is not likely to remain in a drawdown condition during rainy periods.
Why don’t you figure out some beneficial use for giant salvinia so people will want to extract it out of the lake?
Currently, there is no known use for giant salvinia that is economically feasible.
What about the weevils (bugs) that are supposed to eat the giant salvinia?
Salvinia weevils were introduced into two enclosures on the lake in August of 2007. The weevils survived their first winter and their populations increased in the enclosures. Additional weevil infested salvinia was stocked in Lake Bistineau in October of 2008 from nursery ponds near Gheens. A major weevil stocking effort in Lake Bistineau began on June 15, 2009. During the two-week stocking effort, over 78,000 lbs. of giant salvinia infested with over 1.8 million adult weevils was relocated from LSU’s rearing facility located near Gheens to Lake Bistineau.
Will the spray hurt the weevils?
The areas where the weevils have been stocked are not targeted for herbicide applications. The goal is to allow the weevils to reproduce and spread throughout the lake.
Is it safe to use the lake water for irrigation purposes?
Some of the herbicides being used by LDWF spray crews or private contractors have water-use restrictions. Diquat, which is used in some of the foliar herbicide applications, has a 5-day restriction for irrigation purposes. Water treated with Galleon herbicide can be used for irrigation of turf grass at levels under 30 PPB but should not be used to water food crops (vegetable gardens) or ornamentals at levels in excess of 1 PPB. It depends on where on the lake your water intake is located and when herbicide applications have been made in the area. Please contact the District 1 Office for more information at 318-371-3050.
Why don’t you use a mechanical harvester like the ones they have in Texas?
Mechanical harvest and removal of giant salvinia is very expensive and labor intensive. Even the best harvesters can only harvest a couple of acres a day.
Why would the department not consider using salt to treat giant salvinia in Lake Bistineau?
Salt will indeed kill giant salvinia at 10 ppt. However, salt will kill bald cypress at 3 - 4 ppt. To obtain 10 ppt saltwater in Lake Bistineau it would take 4,186,663,988 pounds of salt. Therefore, salt is not a reasonable solution.
Why were the Galleon herbicide treatments curtailed in Lake Bistineau?
Galleon was used to treat giant salvinia at seven sites on an experimental basis. Tests revealed that Galleon rapidly diffused away from six of the seven sites and was essentially ineffective at those sites. Based on theses test results, and in consideration of the approaching drawdown, Galleon treatments were curtailed. Galleon treatments may be considered for use in some locations during the drawdown.
Will Lake Bistineau be closed to recreational fishing activities during the drawdown?
No, these activities do not negatively impact the resources there.

For more information, contact: Evan Thames at 318-371-5216 or ethames@wlf.la.gov [3].