Pond Boss Forums AQUATIC VEGETATION Controlling unwanted plants Need to make Duckweed disappear for short time

Experts, I have a need to make the duckweed disappear but only for a week. I am the manager of the 2 acre municipal lake that is completely covered with duckweed. It is located in the middle of town in a very nice park. The 4th of July weekend is the 100 year anniversary of the town with a big event scheduled all weekend around the lake. So only for the week I was requested to do whatever it takes to clear the lake of duckweed and it only needs to last the week. So is there something I can use to kill all the duckweed and that I would not need DNR approval ? I can get DNR approval but not sure that can be done in time.

Lake condition
It is just over 2 acres. Has no inlet or outlet and is located in the center of town in a municipal park. The average depth is 3’ and is a muck bottom. I have a pump circulating the lake. A very nice aeration pump was just donated. For the anniversary 2 really nice lighted fountains have also been donated. I am in the process of working through all the steps with the DRN to have the lake dredged out. Because of the condition of the lake I know it is not possible to stop the duckweed. I have been doing some manual removal of the duckweed. It is a small percentage that I can remove manually, but all I can remove is that much more the lake does not have to digest. I know until I get it dredged and the proper aeration I will never get it under control.

I have gotten great help and education here previously and I appreciate it. What can I do?

If you aren't too concerned about anything other than clearing it out, just hit it with a copper based product like Cutrine, probably from any local farm store. Dredging the lake and aerating sound like good steps to eventually getting it cleaned up, too. But for now, hit it with a chemical killer immediately and you'll have plenty of time to monitor and manage your results before the celebration week.

You'll probably get some other idea here as well, but that'd be my vote for a quick solution that will probably last more than a week.

It is true I have no concern for anything but clearing the lake. There are no fish left and no plans change that until after dredging.

How fast does it cutrine act on duckweed?

Boy that is tough. Anybody in town going to volunteer a mechanical skimmer for a couple of days? Depth of pond not a real big influence on duckweed. Excessive nutrients are. Since it is floating most contact herbicides are easy to apply. Problem is you really might cause more problems killing it off all at once. I guess if dredging is in your future that does not matter as much. And it sure would have been better to nail it before it took over the entire pond.

I'd probably go with a Diquat product. Reward, Aquacide and others. Diquat dibromide is a fast acting dessicant. My only concern is will it sink or just die? If it floats, back to square one. Put out a flier, volunteers needed for one time get together skimming pond for 4th of July.

The best way to treat DW (absent lake renovation or killing the fish) is with a systemic product like Sonar. That is not your situation however. You have no fish and need speed for a short period.

For that you need a contact (fast acting product) like Reward. Also you have a conundrum in that water agitation (waves , vigorous mixing , wind ) will help kill/reduce DW but it will also make the Reward less effective. The other complicating factor is timing. DW has a nasty advantage in that it produces turions ( seeds which fall into the mud and don't come up and start growth until the surface light hits the bottom). DW can double in volume everyday and with the turions active can cover the pond in a few days time. That is why a total water body product like Sonar works better than a contact product as it covers the whole system for a longer time and thus gets the seeds (most of the time, often a second application is needed).

My suggestion. Be ready to do several things in sequence and have a backup plan.

Get some Reward with an adjuvant (Side Kick II or similar which cuts through the waxy covering on DW)). Start now and spray it with a strong dose. That should kill all the DW it contacts. See how long it takes. Once the water clears be ready to spray again. Keep ahead of the stuff by spraying patches as they appear. A few days before the event start up the fountains for surface movement. Hold off on the aerator as it will help long term but for now it will circulate the turions to the surface which you don't want. About 3-4 days before the event be ready to spray the entire pond again if any DW is present or if a film or sludge type stuff is on the water ( a pre-cursor to a new batch of DW popping up). You could try to combine a Reward application (same time but separate application) with Sonar or White Cap or Habitat (systemics).

There are other things that work but I don't think you want to go there as they are not aquatic approved.

Mechanical skimming is the answer--remove it and move the water with your fountain and aeration for the week and it should be okay.

I've been researching mechanical skimmers for some time and I've seen one work well but it's $6000 www.proskim.com I think it would take the weed out in a day or two and then you'd be all set.

I've inquired if anyone bought one to rent it out or perform the mechanical skimming with this product commercially--nothing yet--you may want to contact them to see if anyone in your area has one.

Other than that people have posted how to make a boom out of rope and swimming noodles and tie straps to pull the duckweed to the side.

I ended up treating with Sonar over a long period which is best to treat before the duckweed starts to appear. This isn't your case.

If you can get the DNR to issue a permit for EWEST's method, that would be my first choice, The Pond Frogs method would be my second choice if the DNR cannot issue a permit in time.

My suggestion for the best solution (although not the cheapest, nor the least labor intensive) is to do PF's skimming first, then ewest's method starting the next day after skimming is completed.

That's an impressive machine! Wonder what would happen if it sucked in a lot of filamentous algae?

Boy, some great info here that has given me a much greater understanding of the options for situations such as this. Is this place a great resource or what??!!

Yes manual removal will help and will work. You will have to keep it up until no more seeds float up. DW can be very heavy in bulk. A seine will also work to reduce the amount.

Manual removal followed by spraying etc will save $ on the amount of chemicals.

The time factor here could be the biggest issue. That is the only reason I said a contact like Diquat. Whatever brand. Stuff works fast and provides immediate results. But ewest is dead on about needing systemics, and slow acting to nail future generations. I saw a pond, not managed by me. Cattails, azolla and duckweed. They Rewarded it to death. Guess what is left? 100% coverage of duckweed. All that stuff in the mud hiding just cameback. Overwinters the same way.

I saw that skimmer product but without actually having used it tough to say. Everyone makes great claims. They are selling. Plus I question availability. And that is a large outlay for one pond. Problem here is you need a sure fire solution.

I'd get as much out mechanically as possible. Day laborers, with the right inexpenive tools can remove the bulk of it. Volunteers are better. It's not a dirty job. Just use tools that let it drain and it is not that heavy. Whatever is left, diquat hard and heavy. And don't sit back and think all done. Keep on top of it until the 4TH. It'a amazing how fast that stuff spreads.

They are experimenting in third world countries with tilipia. The results are being published and great success is achieved. So much so they need farmers for duckweed to feed the fish ponds. And stuff is loaded with nutrients. Jam packed. I think Rutgers is experimenting with it as a food source. If I lived in Texas I'd have some tilipia ponds and duckweed ponds.

Still, mechanical, even with hand tools if needed, then diquat. This is a quick fix only like you asked for. Not a long term solution.

Interesting about the duckweed and Tilapia. When Rex swings by I might put one or 2 in a neighbors pond that is 50% covered with DW just to see what happens. It's probably 50' x 80' with no fish in it other than a few FHM that I threw in there yesterday.

Thank you all for your advice. I am going to apply EWEST suggestion and see what will happen. I have ordered the supplies to get started as soon as possible. In the mean time I will continue the manual removal with all the time I can find.

Speaking of manual removal I have a system that works well. It involves a 3” gas powered sludge pump and a screened box on a utility trailer. I build a primitive pickup skimmer for the intake. I mount the pump to the trailer. It discharges directly into a screen box. When I am done I haul it away and unload it. On days with a breeze I setup at the downwind side of the pond. On regular days I get out the prickly rope and collect it to where I setup. I also found a large landscaping rake with some foam attached to the back of it can help rake the duckweed into the skimmer. The more I can rake into the skimmer the faster it goes.

Sweet set up. I use a wide landscaping rake quite a bit in my business for removal. I like the foam add. If you had access to one of those floating barriers like they are using in the gulf I'd imagine you could direct almost all of it into your take up. As it stands, how much are you removing in a 8 hour day per surface acre? I also have used a lot of trash pumps in my time, would like to see some photos of that screening set up.

How thick is the DW on the surface ? I have seen it up to 8 inches thick. I hope you don't have that situation.

In a normal situation mechanical or tilapia would be my first choices. Then the other methods. You have a different need and mechanical plus contact/Reward (diquat)and an adjuvant are your best chance.

Keep us updated and we will try to help.

Stuff just stacks on itself. The first thing that crosses my mind when I see it on a pond's surface 100% is, how thick is the mat. I have opened a 3 foot by 3 foot hole and have it closed in a couple of minutes. That is a self realization you are way up excrement creek and paddleless. Wineries are calling, wine barrel ponds, planters and fountains. Get to check on my FHM fry also. Yesterday curlyleaf pondweed, matted on the surface. Would almost prefer duckweed to that. Had a pond drop over 2 1/2 feet in 5 weeks. None of my others are close. I know it's a pain but I like photos of rigs I may use someday. If I could drag a long enough boom across a pond I could stack the stuff, but intake to the pump is the how to?