Skylark,

If you really want to knock the southern naiad back you need to use a systemic herbicide like floridone it does take longer to kill but it kills roots and all. Cutrine plus is a contact herbicide so your just killing the tops of the plants. Floridone is expensive and you need a licened applicater to apply it im sure theres someone in AL that can handle that for you. If you want to go with grass carp i would stock 7 to 10 per ac also ducks love to eat southern naiad so get some grass carp and ducks and let them do the work for you.