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... the traditional transplanted method to direct seeding method was taking place particularly at Must rice granary area. The increased usage of fertilizers resulted in the leaching of a certain amount of nutrients into the aquatic ecosystems. A fertilizer that is generally rich in phosphate and nitrate plays an important role in triggering the tremendous growth of floating weeds (Caffrey et.
al 1996). A noticeable feature of rice fields that depend heavily on the use of fertilizer is the occurrence of massive infestation of floating plants such as Salvinia (Oliver 1993). Recently outbreaks of salvinia have been observed throughout the Southern United States. (Jacono 2000). It has been found in water bodies and freshwater drainages of Texas and Louisiana, Alabama, Georgia, Florida, Mississippi, Arizona, California, and Hawaii. As a result the United States has declared the Giant Salvinia a Federal Noxious Weed, meaning that the importation of Salvinia molesta into the United States and transport across state lines is prohibited by Federal Law.
However one problem is that the species must be listed by individual states as a State Noxious Weed in order to be prohibited for sale or cultivation within that state, and in a few states such as Hawaii it is not prohibited (Jacono 2000). This creates a problem the spread of Salvinia. Infestations in Texas ponds have been linked to purchases from local water garden nurseries, which can also be linked to Salvinia's prevalence in the horticultural trade. Sites where giant Salvinia occurs in cultivation can serve as sources for introduction into new regions.
Human transport, including boats, trailers, etc. , will spread the plant locally. There were many early attempts to control Salvinia. They ranged from Chemical control with the use of herbicides to mechanical control measures by manually removal from small water bodies. Both of these attempts proved to be unsuccessful.
Despite the availability of herbicides to kill the weed, attempts to control salvinia chemically have failed to provide long-term solutions. The reason for this is basically economic. For example, at Lake monodrama, Australia, use of AF 101 sprayed from a helicopter was abandoned in 1978 after $ 160, 000 u. s. had been spent. At the time the plant was doubling in size in 3 days, implying the need to kill more than half the infestations every 3 days if control was to be achieved (Thomas and Room 1986).
Economic constraints were also the main reason for failure of physical or mechanical controls. Once the weed is established, biomass es of about 80 tonnes per hectare fresh weight and the potential for rapid regrowth make this impractical. The use of weed harvesting machines was considered in Australia, but was abandoned because the growth of the plants exceeded the removal capacity of the weeds (Thomas and Room 1996). The major breakthrough in Control of Salvinia came on Lake Moondara in Australia, where biological control proved to be successful against Salvinia.
A new beetle species, Cyrtobagous salvinia, was discovered in Salvinia's native brazil that fed exclusively on Salvinia. The beetle was brought to Australia and released where it rapidly destroyed and infestation of kariba weed covering two square kilometers. The beetles most spectacular success occurred in Papua, New Guinea where the beetle consumed two million metric tons of the weed in just two years (Barrett 1989). Other beetle programs are currently under way all over the world.
The success of the beetle is due to the fact that it feeds selectively on growing points, which must be of considerable significance to a plant which relies on vegetative propagation. The larvae tunnel through the rhizome destroying vascular tissue (Thomas and Room 1986). Since Salvinia is asexual, the worlds entire population of the plant is o ostensibly genetically identical. The lack of variation, suggests that the susceptibility of the weed to C. salvinia should not differ from place to place. However, biological control is not perfect and there are a few problems to consider with biological control.
C. salvinia eggs will not hatch below 19 degrees Celsius. Since salvinia will continue to grow at 10 degrees Celsius and can survive light frosts it is clear that the plant will survive in areas which, for part of the year at least, will not support C. salvinia (Thomas and Room 1996).
Salvinia molesta is a rapidly growing plant that has invaded and dominated many non-native areas. It has led to huge economic and socioeconomic costs throughout the world. Control of Salvinia has been achieved in many countries such as Australia, New Guinea, and Malaysia. With the current outbreaks of Salvinia in the southern United States it is important for society in these areas to realize the potential threat to ecosystems. The importance of funding must be realized and made available for programs to successfully achieve control. The concept of biological control is simple, however the usefulness of these biological control agents will probably lie more in the realm of integrated control that includes education of the public as well.
Biological control seems to be the best answer to the current problem for the results seem to be effective, environmentally sound, pollution free, and non-target plants are not affected. Presumably, biological control succeeds if genetic variation is limited. Therefore, clonal propagation, which allows the kariba weed to dominate the world, may provide a way to destroy these noxious invaders. Barret, S. (1989).
Water Weed Invasions. Scientific American, October, 90 - 97. Caffrey, J. M. K. , Barret, P. R.
F. , Murphy, K. J. , Wade, P. M. (1996). Noxious Floating weeds of Malaysia. Hydrobiologia 340: 121 - 196 Jacono, C. (2000) Non indigenous Aquatic Species: Salvinia Molesta.
United States Geological Survey. Feb 10, 2000. (web). Julien, M. H. , Bourne, A. S. , Chan, R. R. (1987).
Effects of Adult and Larval Cyrtobagous Salvinia on the Floating Weed Salvinia Molesta. Journal of Applied Ecology, 24: 935 - 944. Mitchell, D. S. , Thomas, P. A. (1972) Ecology of Waterweeds in the Neotropics.
UNESCO Technical Papers in Hydrology, No. 12. Oliver, J. D. (1993). A review of the biology of giant salvinia (Salvinia Molesta) Journal of Aquatic Plant Management. 31: 227 - 231.
Raven, P. , Evert, P. , Eichhorn, S. 1999. Biology of Plants. Sixth Ed. W. H. Freeman and Company.
New York Room, P. of Salvinia Molesta and Simulations of Bio Control. Journal of Ecology, 76: 826 -M. (1988). Effects of Temp. , Nutrients And A Beetle on Branch Architecture 848.
Seagrave, C. Aquatic Weed Control. 1988. Fishing News Book, Inc. Great Britain. Thomas, P. A... , Room, P.
M. (1986). Taxonomy and control of Salvinia Molesta. Nature, 320, 581 - 584. Bibliography:
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Research essay sample on Invasion Of Molesta Kariba Weed
