Duckweed in a lake

chucko · Jan 8, 2016

Anyone know of something to kill it ?
I found one spray but got sticker shock

oosik · Jan 8, 2016

The fish & game dept around here has experimented with grass carp. I ride by one lake all the time and these carp have completely eliminated all pond weeds on the shore line. This is a fairly big lake too - half mile wide by four miles long. The carp get big - I've seen some that will go 4 to 6 pounds.

ShaleniFarm · Jan 9, 2016

Sonar is what we used. Only thing that worked. VERY expensive. Lasted a few years. Google 'sonar duckweed'.

Good luck!

murphy1244 · Jan 9, 2016

I too use grass carp add 2 every 3 years.

chucko · Jan 11, 2016

ShaleniFarm said:
Sonar is what we used. Only thing that worked. VERY expensive. Lasted a few years. Google 'sonar duckweed'. Good luck!

VERY expensive.very very

comancheflight · Jan 12, 2016

Done this for years..KARMEX. I bought enough for many many years but heard they have discontinued it. I forget the replacement stuff...anyway Karmex comes in 4lb bags. Dissolve a pound in 5 gal bucket water and then disperse putting in about 10 areas over 2 acres. It disperses quickly. Expect around 4 days for duckweed to sink. Once cleaned it only requires about a cup a year to maintain...warning: it will kill all vegetation including catails along the banks and if you have a lot of vegitation it will kill the fish if the plant material dies quickly by depletion of oxygen. If what you have is watermeal then your problem is very serious and Sonar or whitecap is about your only recourse. Some use a lesser amount of whitecap along with reward and have read of some success. This is only if it is watermeal. Watermeal is the smallest flowering plant in the world and doubles in 48 hours...I hope you don't have that. (If you stick your finger in the water and pull it out with what appears to be tiny green dots the size of a pin head - that is watermeal). I have maintained a small lake for over 30 years and Karmex for anything other than watermeal will do the trick.
Sonar can cost $1,000 per acre to treat watermeal..as said, it's expensive.