I need to help a friend remove duckweed that is nearly taking over his little pond. I've heard you can rake it up but that'll take a good bit of time and effort, plus I may not get all the way down to the roots.

It seems I remember dad putting lime in ours but I don't recall if that was to kill vegetation or just to clear the water up.

There are no cows on his place, so if y'all think round up or 24D is safe, I have some of both.

Any other reasonable suggestions or products that you recommend would be appreciated.

Thanks in advance.

Is it a stocked pond? If it is, I would manually remove it. If you do use a chemical treatment, only do about a 1/5 to a 1/4 of the pond at a time.

He does have some fish in it now and wants to add some crappie. Reason why this got brought up because I mentioned that crap will choke out all the oxygen if he leaves it as it sits. He'd waste $ on fish that would ultimately die.

Figured the rake was wear I was headed on this deal, but wanted to reach out just in case someone was more knowledgeable about a product.

You could try Rodeo. But if he wants to add fish treat a little at a time. As the weeds die off, they will sink and start to decompose which will also take oxygen out of the water.

Well I'm an idiot.

Duck.

Duckweed.

It's duckweed, sir.

Put Koi goldfish in your pond.
They will eat your duckweed.
Then when they are big and beautiful, catch them and sell them to a Koi collector.
Profit.

Duckweed rarely chokes out entire water bodies unless its really secluded from the wind. Even if you get rid of it the conditions that brought it will just bring it right back. Leave it alone. The gadwalls love it.

Crappie in a pond may not be a good idea unless it's a big pond.

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He does have some fish in it now and wants to add some crappie. Reason why this got brought up because I mentioned that crap will choke out all the oxygen if he leaves it as it sits. He'd waste $ on fish that would ultimately die.

Figured the rake was wear I was headed on this deal, but wanted to reach out just in case someone was more knowledgeable about a product.

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Wait wait wait wait wait...

the plants will choke out all the oxygen? Seriously?!

Or chemically treating the Lemna sp. will destroy the oxygen values?


Before I say anything I need to know that you and your friend both know that even aquatic plants MAKE OXYGEN and don't "choke it out". The more vegetation in a pond the higher the DO content will be (in most cases), once veg states to die and decay, then the microbes that come in use the available DO to do their work and breakdown the veg.

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Wait wait wait, you do realize duckweed is a floating aquatic plant? I would venture to believe that nearly all the oxygen being produced is at the leaf surface, so very little will make it into the water. Additionally, floating macrophytes limit the exchange between water surface and air, a significant source of DO, as well as reduce sunlight for submerged macrophytes and phytoplankton, the main source of oxygen. It is well documented that other species of floating macrophytes (salvinia, water lettuce, water hyacinth) have a significant impact on DO levels so I don't imagine why duckweed would be any different. So what you said it certainly true regarding submerged macrophytes but is incredibly oversimplified. Simply put, floating macrophytes will not increase the DO in a body of water.

This article below specifically addresses the effects of Lemna on DO but the gist of it is: "Anoxic condition resulted throughout the day in floating plant system. DO varied significantly with depths in oxic condition. DO dynamics in these wetlands can be explained by photosynthesis, respiration, deaeration and reaeration processes."

Lemna effects on DO

Good info to know.

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Crappie in a pond may not be a good idea unless it's a big pond.

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I always hear people say that but we have a pond maybe slightly larger than an acre and crappie do very well in it along with the bass. Maybe an isolated incident though I don't know.

But will they decrease it?

Limiting surface exchange is understandable. But the aquatic veg. isn't going to choke out oxygen from a pond.

From A&M Agrilife extension

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Duckweed colonies provide Habitat for micro invertebrates but if duckweed completely covers the surface of a pond for an extended period it will cause oxygen depletions. These colonies will also eliminate submerged plants by blocking sunlight penetration.

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[url]=http://aquaplant.tamu.edu/plant-identification/alphabetical-index/common-duckweed/[/url]

Yes it can and will. If there is no surface exchange, and no sunlight penetrating to allow submerged macrophytes and phytoplankton to photosynthesize, how else do you presume oxygen will saturate the water? Take a DO reading under a mat of floating vegetation and one in open water and it might surprise you. I'm going to use salvinia here because it is what I am most familiar with.

Study on effects of Salvinia

"Figure 3 shows mean DO levels and changes in percent surface coverage at all six study sites over time. When mean DO level at each percent surface coverage value was regressed as a function of percent surface coverage, the regression equation was y = -0.02x + 4.08, r = -0.67, n = 21 (Figure 4). The negative correlation coefficient (p < 0.001) indicates that there is an inverse relationship between DO level and percent surface coverage. As the biological control agent reduces surface coverage, an increase in DO occurs. Dissolved oxygen levels decline with increasing plant coverage."



Keep in mind anything below 3ppm causes stress to most warmwater species and below 2ppm is typically lethal. For salvinia in this study significant stress would occur at/around 40% coverage and significant mortality at 80% coverage.

Too many aquatic plants in your pond will cause your dissolved oxygen levels to decrease at night when the plants switch from photosynthesis to respiration. Combine that with summer weather and you can have fish kills at night/early morning due to low DO.

Excellent discussion.

You've had that salvinia data a long time... just waiting to use it huh?

I am completely wrong.


I do think that physical removal of the lemna is still your best option.

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I do think that physical removal of the lemna is still your best option.

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And I would agree with this. Duckweed is a relatively easy aquatic plant to control and if you can avoid using chemicals ($$$) then I would suggest that. Anything registered for aquatic use (as in you can't legally just use Roundup as suggested) is expensive because of the rigorous testing process.

I'd like to thank y'all for the info and advice. There are some smart and talented folks on these boards and I appreciate the insight. It appears that old fashion manual labor will be the quickest and most effective solution.

Thanks again fellas.

Crappie can do really well in small ponds. Just make sure they have plenty of forage.

Yes sir. Indeed, he'll have enough to sustain the small amount he hopes to introduce to the pond. The bass in there currently seem to be flourishing, but with the frequent visits by his grand kids, he hoped to give them a smaller fish that is easy to snag with a worm or a minnow. Crappie should do the trick.


Again, you guys are awesome. Best forum on these boards right here!

I had bought a place with a small pond that was completely covered with duckweed. To learn about duckweed (or any pond weeds in Texas) I recommend reading: http://aquaplant.tamu.edu/plant-identification/alphabetical-index/common-duckweed/. Stocking Tilapia in the spring can control duckweed as long as you do not have too many large bass. Otherwise the tilapia make a good forage fish for the bass, but are not as effective controlling the weeds. Tilapia are also fun to catch on a worm. Rather than crappie he might be better off stocking bluegill, which will also feed the bass, but will not take over. At this time the best control is probably raking it. Since it is a floating weed, once you rake it off the surface the root comes with it. Proper herbicide works, but you will want to treat in the spring and add tilapia to each the dead plants so the pond does not turn over. Once the water temperature falls below 50 degrees, the tilapia will die, so you will want to catch as many as you can in the fall.

We use Tribune (diquat dibromide) with a aquatic surfactant (Induce is the one we use) for duck weed. The recommendation to only do 1/4 of the lake at a time is correct.