On Wed, 28 Mar 2007 22:48:55 CST, Kurt
wrote:

Get a big net and periodically scoop it out. Anything that kills it is
going to kill other things.

That may be the only solution. I've avoided that because in my case
it will involve a boat and many hours (perhaps days) of work. The
re-growth rate is so phenomenal that I fear having to do it
continuously because it doesn't get near cold enough here to kill it.
Sonar seems to only get free floating plants, rooted ones should be
quite safe according to the ads. I don't quite understand why you
would have to wait longer to use Sonar-treated water for irrigation
than for drinking, though. Maybe I read it wrong. Florida seems to
be rather touchy about carp in ponds, and what literature I can find
seems to be rather skeptical about the effectiveness of biological
control. My brother is coming down from NC today for my birthday,
maybe I can get him to call folks for me, there's a UF extension not
far from here that might be able to answer questions. I can't talk
too well anymore or I'd make the phone calls myself. My middle pond
has a big aerator in it, and remains duckweed free. I haven't seen
any ducks there but I have seen plenty of ibises (ibi?) and egrets.
Maybe the aerator's agitation of the water has some inhibitive
quality, I really don't know, but I can't remember seeing any in water
that is moving.
--
Galen Hekhuis
"Mistakes were made"