Eradicating duckweed (Lemna minor)

froggy

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Does anyone have a better method than frequent netting-off for eradicating duckweed from apond, or at least keeping it at bay?
 

grunsven

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Reduce nutrient content. Dominance of Lemna minor indicates far to high nurient concentrations.
I do not think there are other solutions.
 

froggy

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The new pond is only big enough for about 3 ducks to fit on, and I think that the local fox would make short work of them.
How can I reduce nutrient content without adding filtration (running electricity to the ponds is not viable)? Are there any aquatic or marginal plants suitable for the small pond that will mop up nutrients?
 

Azhael

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Introducing fast growing plants may pose a competition for Lemna and reduce it´s growth.
However i don´t really undertsnad why Lemna seems to be so annoying for you.
Elodea, Eichornia crassipes, Azolla....are some fast growing plants you could use. However, i don´t think they will erradicate Lemna, they´ll just compete with it, and if they are removed duckweed will probably strike back.
I think your best bet is to net it off, and "clean" the plants with stuck duckweed with a hose, and then net it of again.
 

grunsven

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First question is how did the nutrients get in?

I agree that adding plants to compete with the duckweed would help. But I'd prefer native species. Azolla is defitely not suitable as this fixes nitrogen and makes the problem worse.
Myrrhiophyllum or Potamogeton species should be OK. Just shop around in ponds and lakes in the neighbourhood.

It is also likely to become less of a problem when the pond ages.
 

froggy

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The older pond probably has a nutrient problem because of fallen leaves in the autumn; trees that are not our property have grown up to overhang the pond. We recently revamped the pond and restocked it with plants after a a major dredging, so hopefully things will balance out in time. The new pond is just a normal hole dug in the garden with a butyl liner. We don't use fertilisers in our garden. The duckweed hasn't got a hold yet, so hopefully all the other plants (Elodea, Nymphaea, Potomogeton, water forget-me-not) will outcompete it. I am also removing the little bits that I see.

The duckweed is a problem because it smothers the submerged plants byt blocking out almost all the light. The submerged plants then die, rot and cause the pond ecosystem to collapse, whilst providing more nutrients for the duckweed to grow. I don't mind having a little bit, as it provides cover for amphibians and invertebrates, but I don't want it to smother the pond by becoming too prevalent.

Thanks for the pointers.
 
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benw

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Hi Chris

Duckweed can be a real pain to get rid of as you say, the way i got rid of it was deny it of light by stretching a black sheet across the pond.

It took a couple of weeks, and it did set back the other plants in the pond, but they soon bounced back.

I appreciate it may not be totally practical, but it didnt involve chemicals and the hastle of netting every last bit out!!!


Ben
 

froggy

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Hi Ben

Thats a novel method of getting rid of it - thanks. I may try this in the winter when the emergent plants have died off anyway.

Thanks

Chris
 

Mark

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Chris, I think I may have the answer....

picture.php
 

taapua

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That is an outstanding picture that should probably be considered for the next calendar edition?
 

oceanblue

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A further recommendation as a native boggy semi floating marginal - watercress. It mops up nitrogen very well in my small tanks and grows well in shallow ponds. If there are not sheep to carry liver fluke you can also eat it.

Avoid azolla like the plague. It's like duckweed on steroids.
 

froggy

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Fantastic picture, Mark!
Good tip with the watercress, oceanblue. I may try it along with the sheeting idea.

Chris
 

fishkeeper

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Also, Azolla gets nitrogen from the air...
 

bobberly1

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No plants use nitrogen from the air, that's what fertilizers are for.
 
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