I've sprayed for duckweed in the past and had good luck with Diquat.
A word of caution, if you have fish treat half the pond and wait a
week before doing the other half. The Diquat doesn't hurt the fish
(when used according to the label) but the decomposing weeds will
deplete oxygen from the water.
On Mon, 02 Jun 2003 02:35:08 GMT, "Tim Fischer"
wrote:

I should probably try the ponds group, but I don't subscribe to it so I
thought I'd try here first.

We have a pond, slightly less than 1/4 acre, which has a serious duckweed
infestation issue. Last year when we took over the property, it looked like
a golf green. This year we put in a floating fountain, but the duckweed is
still fighting hard, which sometimes clogs the fountain. I fear by fall it
will be about as bad as last year.

Pulling the stuff out manually is like draining the ocean with a shotglass.
So I fear I'll have to resort to chemical means. So my questions:

1) In doing surfing, it seems that Sonar is the chemical to use, but it's
$$$EXPENSIVE$$$ (I actually saw it for $1900 a gallon!) Second choice is
Reward, which is still expensive but more like $100 a gallon. Anyone have
any experience with this stuff? Does it work?

2) If I *do* chemically treat with Reward, will I have to do it every year?
Or will tackling the problem this year (or a few years) get rid of it for
the most part?

Surfing for info on ponds is difficult, since most postings consider "ponds"
to be like 500 gallons, and ours is much larger.

Thanks!
-Tim