Mr Willy,
I can think of a better way, not cheaper however.
Sonar AS or Q will work very well this time of year, but will be tougher as the season progresses. You can eliminate approx 90% of it this season. The remaining 10% can be left for fish habitat, structure etc.
If there are any other plants you are trying to protect, Sonar would not be the best choice.
My 2 cents,
Mark
