Caddo Lake Invasive Plants




Caddo Lake and other lakes in Texas are facing a major threat from the fast-spreading Giant Salvinia and other invasive plant species. Here we cover the extent of the invasive species problem on Caddo Lake and the measures being undertaken to combat the invasive plants menace on Texas lakes. 

Giant Salvinia is the most invasive plant species on Caddo Lake. It’s a hardy plant with the potential to cover 39 square miles in just three weeks. 

Other invasive plants taking control of Texas reservoirs and water bodies include non-native species such as:

  • Water hyacinth
  • Chinese tallow
  • Nutria
  • Zebra mussels
  • Hydrilla 
  • Yellow and crested floating heart plants

Giant Salvinia on Caddo Lake

Caddo Lake has in the past faced numerous challenges from both natural and man-made causes. It has faced mercury contamination, oil spills, and encroaching water hyacinth. 

However, none of the previous challenges has been as devastating as the threat posed by Giant Salvinia. The invasive species plant has caused both ecological and economic damage to the lifestyle of the people that call Caddo home. 

Some are even comparing it with the sadness of learning that your friend or family has cancer. The plants pose both ecological and economical challenges to the region. In this post, we explore how the giant invasive problem came to Texas, the effects of invasive plants on the ecology and economy of Caddo Lake and other Texas lakes, and what is being done to combat the problem. 

The monsters plaguing Texas water bodies are invasive plants going by peculiar names such as Giant Salvinia, common water hyacinth, zebra mussels, crested floating heart, and yellow floating heart. The army of invasive plant species has in the last few years taken over inland waterways and lakes in the 254 counties of Texas. 

Some of these invasive species are seen as obnoxious weeds but if left unchecked they can gobble up hundreds of acres of water surface area within a short time. 

Others form a thick canopy over the water and outcompete native species, prevent sunlight and air from reaching beneath the water, clog water intakes, hamper boating activities, and generally upset the natural ecosystem. Invasive plants such as Giant Salvinia create multiple problems on Texas lakes that are very expensive to deal with. 

Giant Salvinia is a major threat to any water mass, big or small. According to Australian researchers, with the right conditions, the Giant Salvinia plant can easily cover over 39 square miles of water in a period of just three months. When its advancing front attains maturity, it can create a carpet of vegetation 3 feet wide. It can kill other plants and aquatic life forms on its path by blocking sunlight from reaching the water below and consuming all the available nutrients. 

Native plants and amphibians will struggle to survive and fish will definitely not survive. Recreational activities on the lake come to a halt as the Giant Salvinia's tiny roots clog boat engines or are trapped in propeller blades. 

In other cases, the heavy dense layer of the plant creates a substrate for the growth of other opportunist weeds, which makes it difficult to even know exactly where the lake shore begins.

The first appearance of Giant Salvinia on an East Texas lake was a major red flag to biologists across the state given the damage it could potentially cause if allowed to spread. The rapidly spreading invasive plant first appeared on Caddo Lake in Texas in 2006. 

Many locals started posting questions and inquiries about the plants on fishing websites. Most of them described it as a strange plant growing on the banks of the lake at Jeems Bayou, one of the most popular fishing spots in the northern part of Caddo Lake. 

Some of the locals believed it was a newer form of duckweed, which is another invasive plant species commonly found on swampy wetlands. A few of the locals knew about the huge danger posed by the Giant Salvinia plant when it began increasing its biomass in just a few days. In just a few weeks, the plant, which scientists now call the world's worst weed, had gained a notorious reputation among the Caddo Lake community as a vicious lake-eating monster.

By 2017, the Caddo Lake invasive plants problem had run out of control. Giant Salvinia had covered over 6,000 acres of Caddo Lake. Biologists in Harrison County knew they had a major problem on their hands when the plant started taking even more areas of the lake. 

According to Tim Bister, a geologist with the Texas Parks and Wildlife Department, Giant Salvinia is rated as the worst invasive species you can ever find anywhere because it outcompetes native plants and makes it impossible for fish and other invertebrates to survive under the water. 

The problem is further compounded by the fact that the Giant Salvinia reproduces rapidly covering even more water and leaving behind devastating effects on plant and fish life. Bister says that under the right conditions the plant can double in size in just 4 to 5 days. If left unchecked, the Giant Salvinia can easily take over the entire surface of the water. 

After the warm, dry summer of 2017, which was a perfect growing condition for the plant, the Giant Salvinia had taken over Caddo Lake, Sam Rayburn, Toledo Bend, and the B.A Steinhagen reservoir. The Four Lakes head the largest infestation of the invasive Salvinia in the state of Texas. 


What Exactly is Salvinia and How Does It Affect Texas Lakes?

Giant Salvinia is an invasive plant species native to South America. The plant was first introduced in the United States as an ornamental leafy plant for backyard ponds and fish tanks. On Caddo Lake, Salvinia has been an invasive plague for years. 

It was first seen on Texas waterways in 1998. It’s not known how the plant appeared in a schoolyard pond in Houston in 1998 and later invaded other public waters such as Toledo Bend, which is a vast reservoir a quarter the size of Rhode Island along the Texas border with Louisiana.

In the eight years that followed, Texas and Louisiana officials kept track of the spread of Giant Salvinia in both states. By 2006, the plant was spreading like a wildfire from one lake to another mainly through contaminated boat trailers. It finally infested all water bodies in Louisiana and a third of the lakes in the eastern Texas.

Giant Salvinia has bright green fuzzy and pretty oval leaves. It grows in floating mats on shallow water. The biggest problem with Giant Salvinia is that it prevents light and oxygen from reaching below the water and creates an unlivable habitat for fish. It also makes the waters hard to navigate for boaters. 

The major concern is the speed at which the plant grows. With the right conditions, Giant Salvinia can double its mass in less than a week. For example, just 10 acres of Giant Salvinia can easily become 160 acres within a month.

Caddo Lake, which is the largest natural lake in Texas, suffered the infestation of the Giant Salvinia earlier than the other lakes. The lake straddles across the Texas Louisiana border north of Interstate 20. Caddo is also the only ecosystem in Texas that the Ramsar convention protects, one of just 38 in the country.

The Texas side of the lake is more flooded and forested with towering cypress trees that are hundreds of years old. The trees are usually covered with Spanish moss creating an otherworldly environment that attracts visitors from all over the country. 

In fact, the popular Animal Planet movie Bigfoot was filmed around this area in 2015. Thousands of duck hunters, anglers, kayakers, canoers, and tourists flock to the Caddo Lake region every year. 

The area is also home to celebrities such as Don Henley the co-founder of Eagles and a Rock and Roll Hall of Famer, who owns property on the shores of Caddo Lake. Don Henley is also known to have dedicated $100,000 from the proceeds of his concert at the American Airlines Center in Dallas to the Lake Caddo Institute.


Other Invasive Plants on Caddo Lake

Another threat facing Texas lakes is caused by zebra mussels, an invasive plant species native to Eurasia. Zebra mussels first appeared in the Great Lakes region during the 1980s. They were first discovered in Texas in 2009 at Lake Texoma. Over the years, spread of zebra mussels have traveled across the state at a rapid rate. 

They have been spotted in five of the major Texas river basins and 14 reservoirs including Belton, Austin, Bridgeport, Dean Gilbert, Canyon, Eagle Mountain, Lady Bird, Georgetown, Lake ‘O the Pines, Randell, Stillhouse Hollow, Lake Travis, Livingston, Lewisville, and Ray Roberts

According to the Texas Park and Wildlife Department, zebra mussels can cause serious harm to all forms of aquatic species, breed algal blooms, and leave potentially dangerous sharp shells on rocks. Zebra mussels can also clog water intakes and cause damage to boats and water treatment facilities. Other invasive plant species on Caddo Lake and other Texas lakes include water hyacinth, Chinese tallow, Nutria, Hydrilla, water hyacinth, and yellow and crested floating heart. 

To prevent the further spread of water mussels and other invasive plant species on Texas lakes, boaters are now required by law to ensure that their vessels are completely drained of lake water before leaving or entering any freshwater river or lake. Anyone found transporting any invasive species or violating the law is liable to a fine of $5,000 per violation. 

Texas residents are also required to report any signs of invasive species outside the affected areas to TPWD via telephone number (512) 389-4848 or (409) 698-9121 or via email to [email protected]


Giant Salvinia Across Texas Lakes

Invasive plant species are a great danger for any water body but the Giant Salvinia happens to be the most worrisome of all of them. 

Texas biologists have found that the Giant Salvinia has already infested 18 lakes in Texas including some of the most popular reservoirs such as Caddo Lake, Brandy Branch, B.A Steinhagen, Conroe, Martin Creek, Murvaul, Lake Palestine, Toledo Bend, Nacogdoches, Lake O' The Pines, Sam Rayburn, Sheldon, Raven, Striker, and Timpson among others.

The plant has also been successfully eradicated in a few lakes over the years including Welsh, Wright Patman, Gilmer, Falcon Lake, Lake Athens, and Lake Fork. The chances of eradicating the plant are higher when the new infestation is discovered early enough and contained using herbicide before the plant can take a stronghold on the lake and spread even further. 

However, one-time eradication doesn’t guarantee that Giant Salvinia won't come back later. The plant is extremely hardy and very mobile. It can also be easily transported from one lake to the next through human activities and boat transportation.

Giant Salvinia spreads rapidly under the right growing conditions, especially in summer. The plant’s roots don’t reach the bottom of the lake and it basically floats wherever the wind takes it on the surface of the water. The plant is quite sneaky too. It flourishes well in backwaters which are often inaccessible by boat, which gives it time to flourish well before it’s discovered. It clings to whatever it touches including boat anchors and motors. 

One of the most common ways of Giant Salvinia infestation is by boat trailer transport. The sneaky plant can survive on moist boat trailer bunks for several days and floats away as soon as the trailer comes into contact with water. It only takes one sprig to cause a Giant Salvinia infestation in any lake or water body. 

Giant Salvinia has a devastating effect on both the environment and economic activities such as fishing. It’s the biggest fear for most Texas fishermen since it makes water bodies hard to navigate and drastically reduces the number of available fish. In terms of conservation, Giant Salvinia is one of the major water issues facing Texas waterways. 

Other harmful invasive plant species that pose danger to Texas Waterways include zebra mussels and water hyacinth. At present, Giant Salvinia has taken over 20 lakes in eastern Texas and has also been found on 22 lakes in East and South Texas.

As a shallow and slow-moving lake, Caddo provides the perfect conditions for Giant Salvinia to thrive. In the worst infestation, the plant covered over 6,000 acres of the 25,000 acres of the lake. It left some of the lake’s areas inaccessible for many years. 


Stopping Invasive Species on Caddo Lake

In four years prior to 2018, the Texas legislature has approved $6.3 million as funding for TPWD to combat the aquatic invasive plants menace. 

The TPWD team already has an annual budget of $1.73 million that’s being used to purchase herbicides, spraying equipment, and fuel among other items needed to fight the never-ending menace of Giant Salvinia and other invasive species plants on Texas lakes.

The funds are also used in developing mitigation measures to stop the spread of invasive species. The project focuses on multiple control methods including chemical, biological, and mechanical means. 

The other goal of the project is to find out the most effective control methods and include them in nationwide projects and initiatives like the Field Office Technical Guide of the USDA Natural Resources Conservation Service and educational program materials of the AgriLife Extension to help both public and private entities solve the invasive plant species problem on water bodies using proven methodologies. 

Mother Nature

Mitigation efforts to control the spread of the plant have started to bear fruit. Just before the growing season in Texas, there were only 1,500 acres of Giant Salvinia in Texas. The severe cold weather in East Texas helps to knock back the plant and slow down its summer growth. However, this wasn’t enough to stop the plant. 

Mother Nature has also played a key role in containing the spread of the invasive species plant. Flooding events and high winds always flush the vegetation from the inaccessible backwaters to the lake where the problem can be tackled more effectively. Flood events combined with cold winters have helped Caddo Lake eliminate a significant amount of Giant Salvinia.

Research studies have also shown that the plant dies when exposed to a 3-degree temperature for a period of 48 hours. In 2018, the temperature in Houston Texas dropped significantly creating sub-freezing conditions for as long as 48 hours. This helps to curtail the growth of the plant but in 2019 the temperatures dipped into the 20s a few times and later warmed up quickly which didn't help a lot to kill the plant.

Mother Nature does her part in eliminating the plant but it’s not enough to completely eliminate Giant Salvinia. Most experts agree that chemical treatment is the best control. However, chemical treatment doesn’t come cheap. Estimates show that it costs around $50 to spray an acre, which puts the cost of complete treatment well over $250,000. 

Herbicides for Invasive Plants on Caddo Lake

Different types of herbicides have been used to kill and stop the spread of Giant Salvinia on Caddo Lake since 2006. In the past few years, spraying contractors have been using a cocktail of glyphosate mixed with flumioxazin or flumioxazin mixed with penoxsulam for Spring to Fall spraying. A mixture of flumioxazin and diquat is used in the cold months of winter. 

However, given the huge amount of chemicals used to kill Giant Salvinia over the years concerns are being raised over the effect of the chemicals on the quality of water and the survival of fish and other aquatic life-forms. 

The Caddo Lake Institute and the Northeast Texas Municipal Water District have conducted water tests and no harmful effect has been found so far. Experts say that the herbicides are normally broken down in waters with high organic matter, sunlight, and bacteria to ensure that the chemicals don’t have adverse effects on the water. 

Biologists further explain that the herbicides being used on Caddo Lake are usually mixed with 100 gallons of water and sprayed directly on the Giant Salvinia plants to ensure that very little of the herbicide reaches the water, as it is broken down quickly and therefore not detectable.

Herbicide treatments are normally conducted throughout the year at Caddo Lake. This has been going on since 2016. Coupled with winter-time treatments, which help to slow down Salvinia growth and recovery during the cold weather, Caddo Lake is gradually starting to get some breathing space. 

Wintertime treatments have allowed conservation efforts to stay ahead of the plants spread on other small reservoirs such as Sheldon, Martin Creek, Brandy Branch, Athens, Murvaul, Fork, Naconiche, and Raven.

The major problem with Caddo Lake is that the airboats used in spraying the plant cannot get through all the brush and timber on most lakes in East Texas, which makes it difficult to ensure that all the Giant Salvinia has been killed.

Giant Salvinia Weevils

Biologists have also been allocated funds to use on rearing Giant Salvinia weevils. The tiny insects help to kill Giant Salvinia by eating and reproducing on the plant’s leaves. 

When their eggs hatch, the insects’ larvae burrow into the stem of the plant which causes the plant to die. The plan to use the weevils came from Australia, where the same plant had arrived the same way it had in the United States through imported garden water. 

In an effort to stop the fast-spreading plant, Queensland researchers went back to the plant’s origins and tested Brazilian weevils which showed a high appetite for Giant Salvinia alone. In 1981, the Nature scientific journal reported that the weevils were showing great effectiveness in eliminating Giant Salvinia in all test lakes. 

Australia was eventually able to contain the problem of Giant Salvinia. Similar stories of success have also been reported in other parts of the world as well as the southern part of the United States. At present, more than 300,000 weevils have already been released into Caddo Lake. 

The Weevils reproduce fast and spread rapidly feeding on Sylvania on every part of the lake. The authorities have stepped up efforts to release more Giant Salvinia Weevils, especially in areas where herbicide bots cannot access. However, the cold winter weather that helps to slow down the spread of Giant Salvinia also kills the Weevils. 

The good news is that presently there’s a more cultural and Giant Salvinia Weevil which is still in quarantine other standard protocol to ensure that biocontrol agents don’t destroy native crops when released. The cold-tolerant Giant Salvinia weevils are expected to be released anytime soon. There will be a game-changer if they can do the job and tolerate the cold weather at Lake Caddo.

The danger posed by invasive plant species on Texas water bodies is a concern for all. The Giant Salvinia, for instance, has a devastating effect on both the region's ecology and economy. 

The last thing anyone needs, especially boaters and fishermen, is to see the lake shoreline being depleted by the plants. Fishermen and boaters have made it a habit to always check their boat trailers at the end of the day to ensure that they haven’t brought any of the plants to the show.

Caddo Lake residents have continued to combat the spread of Giant Salvinia in every possible way. There was even a report of a resident who took a 2,000-degree blowtorch to incinerate a metal tub full of the plant. Although the plant seemed to have burned down and died, green sprouts started emerging from black ashes a week later. Like the proverbial phoenix that rose again from the ashes, the Giant Salvinia fully grew back in just three weeks. 

The invasive species problem is costly too. The state of Texas has already spent over $3 million in herbicide application in all the affected lakes. Caddo alone has spent 40% of the $3 million. The herbicides must, however, be sprayed repeatedly without stopping because the plants are constantly pushed by wind and currents back to the previously treated areas. 


Final Thoughts on Invasive Species at Caddo Lake

Keeping Giant Salvinia Caddo Lake infestation from reaching other lakes has become a joint project for Texas and other neighboring states such as Louisiana because of the rapid spread of invasive species and their ability to outcompete and take over other native water plants and life-forms. 

If nothing is done to stop the Giant Salvinia at Caddo Lake, the plant will take over and kill much of the lake’s ecosystem leaving behind a devastating effect on the region’s economic activities such as tourism, fishing, and recreational boating. 

The on-going battle against Giant Salvinia in Caddo Lake was highlighted in a recent documentary called Something in the Water. 

There’s still a lot to be done to completely eliminate Giant Salvinia and other invasive plant species from Texas lakes but the combined efforts of herbicides and armies of Giant Salvinia weevils, aided by Mother Nature, are starting to bear fruit in the war to save Texas water bodies. 

Public awareness and helping the Texas Parks and Wildlife Department (TPWD) in reporting outbreaks remain the most effective first line of defense against Giant Salvinia and other invasive plant species on Texas Waterways.




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