By all means use biological ...
By all means use biological control if cost is an issue. The water hyacinth weevil ( Neochetina eichhornia) has already been used in Africa's Lake Victoria for this purpose. It takes a few years following introduction to gain control, but it does work. I imaging scientists on Lake Victoria would be willing to capture adult weevils for you to inoculate your lake with an initial breeding population of 1,000 or so in cups containing 50 each.
I worked on a large (about 45,000 ha) lake in Florida that, by the early 1970's, received a high volume of treated sewage rich in phosphorus that helped produce about 4,500 ha of water hyacinth 'mats' in the lake's 21,000 ha littoral zone. These mats shaded and destroyed biologically important native plants and associated fish and wildlife and left thick organic deposits on the shallow lake bottom. We applied for and received the very first batch of 300 hyacinth weevils divided into six styrofoam coffee cups for release at six locations. These had been cleared for use and provided by the U.S. Department of Agriculture after that agency determined the only plant they fed on was the water hyacinth.
The weevils reproduce slowly, so it took about three years to see widespread visible damage the hyacinths in the release areas were visibly stressed and did not flower. A couple more years and all the hyacinths in the lake were stressed and did not flower. After seven years all the hyacinths were stunted and dying, and by year nine there were very few left. The same happened in other release lakes in both Florida and Louisiana.
You may want to test these against your native aquatic plants and agricultural crops, or you can do a search of scientific journals to see if there are any reports of the weevil feeding on other plants.
The weevil replaced chemical spraying (the hyacinths were spreading faster than chemical sprays killed them) and harvesting was far to expensive to consider. The temperatures in Florida ranged from summer highs above 40 degrees C to winter lows of -10 degrees C. These extremes did not seem to adversely affect weevil populations.
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Dear sir; I realize you have little to no knowledge of modern microbiology. So may I update your understanding of what you commented on. The clean and long term control of all waste and invasive plants is called "Bioremediation" In the early 1970,s they tried to use bacteria and some helpful fungi. They were effective but the time took way too long and the end results were an un finished process. The reason was bacteria and fungi are DNA microbes. They do not have the genetic code for reducing compounds into their elemental/nutritional state. Only the RNA microbial group called Archaea can do this. Their activity rate of propagation is once every 20 minutes. An ocean spill takes 12 hours. The land will take no more then six weeks instead of years. Results = 100% completion, extremely low cost, and very quick clean up time. best of all no chemicals of any kind. RNA microbes are non pathogenic and non mutational. They are safe for the environment, the animals, fish, plants, and people. Largest users are farmers.
Published by Guy McGowen, President/CEO/Chief Science Officer