Now this is an old thread brought back to life!
I'm not an expert. I can't give you control measures. Others will be along shortly that can help you. But I can give you some things to think about in your process of getting rid of an unwanted weed.
The weed is there for a reason. There are unused nutrients it is taking advantage of.
If you kill it, some other natural process will take advantage of the nutrients the pond weed is now using. It might be more or even less desirable to what you have now. Just something to keep in mind.
For example, if the pond weed is eradicated, the nutrients might create a huge algae bloom. That could be great for the fish, but your pond might turn a completely different shade of green than it is now and suddenly no longer be as clear as it is (if it is clear now). The pondweed might be replaced by some other weed that the birds bring in. I don't know how many different weeds grow in a pond, but it is a high number. Something will try to use the nutrients available. You might end up with something much less desirable as what you have now.
Man, I'm sounding like a downer. Don't mean to sound that way, just wanting you to be able to "think ahead" in that once you get this weed eliminated or at least under better control, it might introduce other issues. Having thought about the potential ahead of time can allow you to plan better instead of jumping from the fire into the frying pan, so to speak.
Hope this helps. The ones who actually know what they are talking about will be along shortly.
