Preventative measures: A Risk assessment of
Pistia stratiotes for Australia was prepared by Pacific Island Ecosystems at Risk (PIER)
using the Australian risk assessment system (Pheloung, 1995). The result is a score of 18 and a recommendation of: reject the plant for import (Australia) or
species likely to be a pest (Pacific).
Physical: The most common physical control method is raking or seining it (using a large fishing net) from the pond’s surface. In the United States, raking is done by mechanical harvesters. The plant is then removed from waterways to the shore where it is cut up by chopping machines and disposed of by spraying across the water (Ramey, 2001).
Chemical: Chemical control methods that have been successful in treating P. stratiotes include the herbicide endothall, which can act quickly and kill all plant cells that it contacts.
Biological: According to Rivers (2002), water lettuce leaf weevil (Neohydronomus affinis) is a native species of South America and was first introduced into Australia in the early 1980's for biocontrol of P. stratiotes. Additional releases of this weevil for research are currently being conducted. These weevils have a very short life cycle (approximately 30 days), which allows for quick establishment of populations. Adult weevils feed on the leaf, while the larvae attack the inside of the leaf. The other effective method of controlling P. stratiotes is the introduction of the water lettuce leaf moth (Spodoptera pectinicornis). The moth is native to Thailand and was imported into Florida for the biological control of water lettuce. The moth has a very short life cycle (approximately 35 days), with the larval stage lasting 17-20 days. The adult moth does not feed on water lettuce, however, moth larvae are capable of inflicting significant damage to P. stratiotes. The larvae are fairly large, which means that fewer larvae can provide a greater effect.
Location Specific Management Information
A biological control programme for Pistia stratiodes was undertaken simultaneously with programmes for the other aquatic invaders Eichhornia crassipes, Salvinia molesta and Hydrilla verticillata, to avoid the increase of other invasive species as one was controlled.
Plants were removed by hand from the two sites where Pistia was deliberately planted.
Reunion (La Réunion)
A program of biological control of water hyacinth and water lettuce on l’etang du Gol has been underway since 2006 (Le Bourgeois & Lebreton, 2006).
2. Gee II, David E., pers. comm. 2006. Wildlife Biologist, Guam Division of Aquatic & Wildlife Resources and Guam team member of the Pacific Invasives Learning Network (PILN).
3. Hilhorst, M. Water lettuce .
Summary: A report on how P. stratiotes was eradicated from the two sites where it was deliberatly planted.
Available at www.biodiv.org [Accessed 24 September 2003]
5. National Pest Plant Accord, 2001. Biosecurity New Zealand.
Summary: The National Pest Plant Accord is a cooperative agreement between regional councils and government departments with biosecurity responsibilities. Under the accord, regional councils will undertake surveillance to prevent the commercial sale and/or distribution of an agreed list of pest plants.
Available from: http://www.biosecurity.govt.nz/pests-diseases/plants/accord.htm [Accessed 11 August 2005]
9. Swaziland's Alien Plants Database., Undated. Pistia stratiotes
Summary: A database of Swaziland's alien plant species.
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