Aquatic Invasive Species

WATER PRIMROSE

Although the yellow flowers and green leaves of the water primrose (Ludwigia hexapetala) seem harmless, the native of South America has become a growing problem within the waterways of South Carolina, and is now included on the state’s list of aquatic plants illegal to own, import, or sell within the state. Distinguished by showy its yellow flowers and a tendency to form dense mats along the edges of bodies of water, the plant spreads both through fragmentation and transport and through the production of seeds. The former method, coupled with its fast growth, adds to its threat as an invasive species. If a piece of water primrose breaks and attaches to a boat or animal, it can then be transported to other bodies of water that were previously uninfected. In its new environment, the plant can spread and form a new mat, which often out competes native species for sunlight and space and can sometimes quickly destroy the ecological diversity of a lake or stream.

Similar to some other aquatic invasive plant species, water primrose can spread from place to place relatively easily through human and animal activity and is difficult to control. However, according to the State of Washington Noxious Weed Control Board, physically removing the plant or covering it with material that prevents sunlight from reaching the plant may be effective ways of slowing its growth and controlling populations. However, physical solutions are costly and not always effective, since the plant grows quickly and can reclaim a body of water within weeks if specimens are left behind. Chemical methods could potentially harm native plants as well as the target species, despite their attractiveness and apparent ease of use. Prevention is therefore the best method of controlling water primrose’s spread. Encouraging (or even requiring) boaters and fishermen to remove the plant from their boats, ballast water, and lines could spread non-animal transport of plant fragments to places that were previously not infested.

The problems of the water primrose are similar to other problematic species. It is aggressive, and spreads easily from one habit to another. Based on the states of Washington and South Carolina, the best method of preventing the plant from taking over native habitats seems to be preventing its spread and establishment. Once it takes over, the plant is nearly impossible to control. Although use of herbicide seems like a simple solution, it is fraught with problems. A herbicide (like Rodeo) effects not only non native plants like water primrose, but also native plants that are already being out competed by invasive species. Also, plants can form a resistance to herbicides over time, leaving the ineffective. This leads to a series of questions. First, is it possible to tailor an herbicide to specifically target water primrose? This is probable, but leaves other questions. Would a tailor-made herbicide be both economically feasible and non harmful to other parts of the aquatic environment? This second question is improbable. New herbicides often have unforeseen effects on the environment as a whole, and may or may not be effective. Means of preventing the spread of water primrose are also problematic. Although the plant is classified as illegal to possess in the state of South Carolina, departments like Natural Resources are often under funded, leading to problems with enforcement. Without enforcement, the law means little. The plant will still spread regardless of regulations. Voluntary measures like cleaning the bottoms and ballast areas of boats are also encouraged, but have the same problem. There is no extrinsic incentive for most boaters and fishermen to go to the trouble of removing the plant. Until there is more of an incentive to comply with these suggestions, there will be little hope in controlling the spread of water primrose.

http://www.ecy.wa.gov/programs/wq/plants/weeds/waterprimrose.html

http://www.dnr.sc.gov/invasiveweeds/primrose.html

http://plants.usda.gov/java/profile?symbol=LUGRH

http://www.ecy.wa.gov/Programs/wq/plants/plantid2/descriptions/ludhex.html

http://www.nwcb.wa.gov/weed_info/Written_findings/Ludwigia_hexapetala.html