enescent, its rhizome segment breaks and the colony fragments into daughter colonies of unequal sizes. It is this mode of clonal propagation that help the weeds grow rapidly over large areas. As wind or water currents disperse fragments, colonies can expand rapidly over vast open stretches on water surface due to the floating nature of Salvinia (Barrett 1987). Freed from competition with other plants and guaranteed almost unlimited space, nutrients, and sunlight, the kariba weed grow and multiply at an extraordinarily pace to achieve some of the highest biomass production in the plant world. Salvinia has been know to double in size in as little as 2.2 days (Thomas and Room 1986). It can quickly cover lakes and slow-moving rivers with mats up to 1 metre thick. Factors which promote the formation of permanent mats appear to be the same as the plant's native environment and in situations where it is a troublesome invading species. They require good light conditions and the optimal temperature for growth is between 25-30 degrees Celsius. The size and growth of these plants ultimately depends on nutrients. If considerable quantities of nutrients, especially nitrogen, are supplied, growth can be very rapid and dense mats are soon formed (Mitchell and Thomas 1972).
             It is this growth rate of Salvinia that has caused such horrendous ecological and economical difficulties around the world. Thick mats of salvinia prevent the passage of large diesel-powered boats and even a single layer of plants is a major obstacle to paddle-powered canoes. As a result, transport by water and commercial and recreational fishing can be severely impeded or halted. Mats block access to drinking water by humans, domestic stock, and wildlife, clog irrigation and drainage canals, and during floods, sweep fences and other light structures before them (Thomas and Room 1986). The plant is a major weed of rice and harbors the host of human diseases ...