I am NOT an aquatic vegetation expert!
However, I have been very impressed with the selective herbicide targeting of some of the products I have used recently.
For example, I sprayed a few gallons of Crossbow (2,4d with triclopyr) this summer on some bad poison ivy areas. I went back and checked results 8 days later. The poison ivy was all scorched to death - and the eight varieties of prairie grass that I also sprayed were showing no effects at all in that time frame.
Crossbow is designed for woody species in permanent grass pastures. If your targeted aquatic plants are truly "woody" species, and your desirable plants are not, then you might have a chance of selective treatment - with the right product.
** I do not know the proper classification of your targeted aquatic plants versus the desirable plants.
*** Crossbow is toxic to fish! (I think due to the 2,4d component.) My point is that you should keep searching (and perhaps spot testing) to see if there is a product that will perform the selective treatment you desire.
Good luck on your project!
