What exactly is Giant Salvinia?
Giant Salvinia is a floating aquatic fern from southern Brazil. It is theorized that it made its way to the United States via the aquarium and water garden industry.
Why is it a bad thing?
Salvinia is capable of exponential growth. In laboratory conditions it has been found that a single plant can cover 40 square miles or about 25,000 surface acres in a 3 month period.
What impact does this have on the environment?
Because it grows so fast it can quickly cover a body of water. Sunlight cannot penetrate through a mat of salvinia and so the water underneath becomes devoid of dissolved oxygen. Without dissolved oxygen fish cannot survive under the mat.
Also, some of the plants die off during the year whether from old age, cold weather, herbicide applications or biological treatments. When these plants die they fall to the bottom of the lake and make the lake more shallow is some areas.
How did it get in Caddo Lake?
Giant Salvinia was first discovered in the lake in 2006. It most likely was brought to Caddo Lake via boat trailers. This is how the plant travels from lake to lake. One plant on a boat trailer could lead to the infestation of another lake. It is absolutely vital that everyone who boats on a lake take the time to Clean, Drain and Dry their boat after they take it out of the lake and before it is launched at another lake. This is the only way to keep if from continuing to spread across the south.
What steps are being taken to combat it at Caddo?
There are 4 basic ways to lessen the impact once it is in a lake and also to try and prevent its spread to other bodies of water: Outreach and Education. Physical Removal, Herbicide Applications and Biological Control
Texas Parks and Wildlife has undertaken a huge ad campaign (Outreach and Education) to make boaters aware of salvinia and other invasives like Zebra Mussels that are also transported by boat from lake to lake.
Physical removal was attempted at Caddo using a barge with a conveyor system on it. Salvinia is very heavy, it is 98% water. An acre of plants weighs around 20 TONS! At this time it is not considered a viable method to combat the plant at Caddo.
Texas Parks and Wildlife has an ongoing herbicide application program going at Caddo, as well as many other lakes in Texas. These herbicides are labeled as safe to use in aquatic environments. Herbicides offer a fairly quick kill time and are used to lessen the amount of salvinia on a given water body as well as a spot treatment to maintain navigation along boat roads and in front of boat ramps.
Biological treatments take longer to work. The idea is to take an insect that is a natural enemy of salvinia and place it on the mat of plants to allow the insect to eat the plant and retard its growth. The Giant Salvinia Weevil is the approved biocontrol agent here in Texas. This insect is plant specific, meaning it has been thoroughly tested by the USDA to ensure it will not eat plants other than Giant Salvinia.
Are weevils being used at Caddo?
Do the weevils work?
Weevils are very effective against salvinia in Tropical and Subtropical environments. Caddo Lake is a more temperate climate and is on the northern limit of both salvinia and the weevils. Weevils can survive an average winter at Caddo but if the weather is below normal for extended times they do not do as well. The salvinia is slightly more cold-hearty than the weevil so the plant survives our winters a little better than the weevil. This is the reason they are grown in greenhouses. The weevils are able to overwinter in the greenhouse and can be out on the lake in the spring when the water reaches 68-70 degrees. Also, in this northern range CBA and TPWD use what is called an integrated pest management program combining the use of herbicides and weevils to maximize the suppression efforts again salvinia.
Can you put weevils out at my dock?
There are a number of factors to consider before weevils are released into an area. The mat of salvinia has to be large enough to support a reproducing population of weevils, (you cannot put them on a few scattered plants). Also, it can take several years for weevil populations to grow enough to begin to control a given area so the area should not be one that is on the herbicide spray schedule for TPWD. CBA coordinates with TPWD on weevil releases to make sure they know where they are so they can avoid spraying the area.