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Home , Salvinia

By Bob Pitman

Giant Salvinia Invasive creates giant headache in the South

It is not a field. This east-Texas bayou is covered with the invasive giant salvinia. Its scientific name couldn’t be more it rages out of control spreading over appropriate: . This water surfaces, doubling the area it floating plant has a predilection for can cover in as little as five days. It is being a problem. It’s often called “the an invasive floating native only to world’s worst aquatic weed” for good Brazil. It has become a giant problem reasons. In common terms, it’s known in Texas and Louisiana where it was as giant salvinia. unintentionally introduced. The plant threatens all southern-tier states Giant salvinia isn’t a towering plant, where warmer conditions suit the but it grows voluminous. Unchecked, plant. In the last 70 years it has been

16 Eddies Summer/Fall 2010 the plant made its way into the open waters of Texas in 1998.

Once established in open water, boat movement most likely spread plant fragments to several east-Texas lakes including Toledo Bend, Caddo, Conroe, and Sam Rayburn, as well as to several Louisiana lakes. Anglers and boaters lost open water and fishing opportunities, and related Unchecked, businesses lost some livelihood. Ducks lost habitat, and lake-front it rages out property dropped in value. of control Here is something else to consider. Giant salvinia is a big financial burden spreading over for state fish and game agencies, as they are forced to deal with yet water surfaces, another stressor on natural resources management. Recently, Louisiana doubling the managers began partially draining popular Lake Bistineau to improve area it can cover giant salvinia control. The drawdown may last throughout 2011. in as little as

A single plant of giant salvinia five days. consists of a horizontal stem floating just below the surface with two thumb-sized emergent green leaves …A single plant covered with short hairs that are joined at the tips, resembling an has been known eggbeater. A modified third leaf is brown, highly divided and dangles to cover forty below the water surface resembling roots. Leaf pairs are produced at square miles of Department each node growing ropes of giant salvinia. The prolific plant reproduces water in three Wildlife by fragmenting. Pieces grow into

Giant Salvinia and entirely new . Individual plants months. or floating fragments are readily Invasive plant creates giant headache in the South Parks dispersed by wind, water currents,

Texas or people. The plant easily invades It is not a field. This east-Texas bayou is covered with the invasive giant salvinia. new locations. Giant salvinia is native to Brazil’s temperate waters and can spread by people to Australia, New survive some winter freezing but Zealand, , India, and Papua will not persist where surface ice New Guinea. forms. With optimum conditions of temperature, sunlight and nutrients, You may have seen it by its market the plant grows at an astonishing name, “koi kandy,” where it has been rate. A single plant has been known popularly sold to aquarium owners to cover forty square miles of water in for several decades. The aquarium or three months. aqua-garden trade is probably how

Vol. 3, No. 2 Reflections on Fisheries Conservation Aquarium owners and aqua- purposeful importation. However, naturally co-exist in nature in Brazil, gardeners desire giant salvinia the loose net of federal and state the so named since it eats the because it is persistent, hard to kill, regulations and authorities used to plant. The weevil has successfully easily shipped with minimal expense block invasive distributions controlled giant salvinia around the and guaranteed to arrive alive to and movements were not sufficient world. customers. Unfortunately, these to prevent the inevitable release of are also classic qualities inherent giant salvinia. It is now, and probably Scientists have researched, reared, to invasive species. Giant salvinia forever, a permanent challenge to and released the control weevil in is a notorious hitchhiker. Suppliers conservation in the southern U.S. Texas and Louisiana for a decade, often unintentionally send it, if only but with limited success so far. fragments, in shipments of other Giant salvinia is a serious invasive Giant salvinia spreads quicker than requested aquatic plants. species, but it does have some the weevil can eat, or the bug can weakness. reproduce. Winter weather sets the Australian researcher Dr. David weevil back, more than it does giant Mitchell scientifically described Present controls involve spray crews salvinia. A control strategy it seems, Salvinia molesta in the early 1970s. regularly treating giant salvinia mats will include , herbicides and He appropriately named the species with herbicides to temporarily reduce mechanical removal. “molesta” to emphasize what he coverage. Only in rare circumstances had seen this plant do to waters in do herbicides provide long-term Giant salvinia is only one among a Australia, Africa and Papua New relief. Mechanical controls are also list of other aquatic invasive plants. Guinea. The U.S. Department very costly and temporary. Giant One thing they almost all have in of Agriculture responded to his salvinia control may ultimately be common is that invasions of these warning and listed Salvinia molesta achieved by the herbivorous salvinia plants cost much money to control— as a Noxious Weed to prevent its weevil. The weevil and the plant not eradicate, but control. Federal Department Wildlife and Parks Texas The salvinia weevil shows promise in controlling giant salvinia, especially when combined with mechanical and chemical controls.

18 Eddies Summer/Fall 2010 Department Wildlife and Parks Texas Cypress trees, up to their knees in giant salvinia, is a sign that fish and waterfowl habitats are compromised. Restoring habitat will be no easy or inexpensive task. and state agencies, universities and Caddo, or Conroe, who deal with stakeholder groups are increasingly giant salvinia year after year. Anyone working together to control the plant. who uses water for work or play should understand the consequences Hydrilla and Eurasian water milfoil of their actions. Responsible users are two such examples. Both are help protect our water and that which native to and Europe. Hydrilla lives in it, on it, or near it. F forms extremely dense colonies growing from bottom to surface in water up to 20 feet deep. Water Bob Pitman retired as a fishery biologist milfoil forms dense colonies from from the U.S. Fish and Wildlife Service in the bottom to the surface, the 2010. Pitman exemplified a commitment to colonies making boating and angling conservation, working on invasive species impossible. Hydrilla has its “Typhoid issues for over a decade. He’s headed to Mary,” tracing its origin in the Montana, where he went to college years ago U.S. to one aquarium dumped in a and minored in fisheries science and majored Florida canal by one person. This in flyfishing. irreversible action will have ecological and economic costs that will never go away.

Prevention is cheaper than the cure, to paraphrase the old adage. Just ask home owners near Lakes Bistineau,

Vol. 3, No. 2 Reflections on Fisheries Conservation