Duck weed

[honeybee]

Following a days water vole trapping I was wondering if anyone can help. The small artificial lakes are almost totally covered in duck weed. Short of getting in the boat and skimming it off and risking falling in,(would also take forever) is there anything that can be done / used to get rid of this. We don't want to use chemicals which is one option. I know barley straw is good for getting rid of blue-green algae. Cheers.

[aeshna5]

Barley straw won't work for duckweed, as former contains natural algicide, but no effect on higher plants (duckweed is a flowering plant). I don't know of any specific herbicides for duckweed + most others would probably kill other pond plants. Skimming seems to be the option. At least the growth rate should slow down now as days get shorter.

[henrya]

I don't think there is much point in taking off the duckweed - it'll only grow again in the short term until it reaches an equilibrium with the environment. Is it causing a problem?

henrya

[fbcpmike]

Originally Posted by henrya

I don't think there is much point in taking off the duckweed - it'll only grow again in the short term until it reaches an equilibrium with the environment.henrya

You cannot control Duckweed by skimming. The plant multiplies by division and rapidly expands untill it reaches some sort of balance in the water body. It will become very dense and whilst it will help somewhat to combat evaporation, it can reduce the oxygen levels to serious levels in hot weather. It can be kept in some control by Swans and Geese who will eat it, but if the water body is large enough it still retains a foothold. So far the only way to remove it is to hope for a really hard winter and a prolonged cold snap that freezes the water to several inches in depth, that will kill it.

We have had this pest for the last couple of years now and we are at our wits end, last winter nearly did for it, with only a couple of square inches left in the spring. Our Geese and lone Swan did a spendid job of keeping it under control, untill the really hot weather arrived, it then covered the whole pond (0.75 acre) in days. Some "helpfull" neighbours and the council tried skimming, but all you do is create a hole for it to expand into within hours.

Pray it never gets into your pond, if it does then pray for a big freeze.

The water voles will not mind the duckweed as was seen on a recent BBc program, the fish will if it gets hot.

[honeybee]

Thanks for your replies guys...
The person in charge of the project was told she could use some chemical to kill the weed but naturally she's reluctant as she doesn't know what knock-on effects could be caused. There are a couple of medium sized lakes linked together and a pond. The lakes are 90% covered. There are a few swans there. The wind blows it and makes gaps in it. We're really worried it's gonna kill off everything under the surface / cause probs.

[henrya]

Unless there is a chemical that's specific to duckweed, use of chemical control is likely to cause more problems than it solves. I think it'll probably reach some sort of equilibrium by itself, though it may take a year or two.

henrya

[fbcpmike]

Originally Posted by honeybee

Thanks for your replies guys...The person in charge of the project was told she could use some chemical to kill the weed but naturally she's reluctant as she doesn't know what knock-on effects could be caused. There are a couple of medium sized lakes linked together and a pond.

I'd like to know what the chemical is if it exists.

Usually there are regulations about using chemicals within certain distances of ponds and water courses, you will have to talk to the Environment Agency before you go ahead as you may need a licence.

Originally Posted by honeybee

The lakes are 90% covered. There are a few swans there. The wind blows it and makes gaps in it. We're really worried it's gonna kill off everything under the surface / cause probs.

It's a floating plant so is moved by winds and other effects, as for killing off, we still have our fish but lost a couple of large ones because of the oxygen levels.

Let us know how you get on, it's a problem in many places and info is always usefull.

[honeybee]

I will try to find out about the chemical and let you know what happens. Cheers

[Dogghound]

A potential solution to this problem would be to stock grass carp Ctenopharyngodon idella these fish do show a preference to eating duckweed as well as algae, and are exclusively herbivorous! these are a good organic way to control the weed, HOWEVER it is vital that you stock GRASS carp and not normal carp Cyprinus carpio as these could have large negative affects on other pond life!

[henrya]

Originally Posted by Dogghound

A potential solution to this problem would be to stock grass carp Ctenopharyngodon idella these fish do show a preference to eating duckweed as well as algae, and are exclusively herbivorous! these are a good organic way to control the weed, HOWEVER it is vital that you stock GRASS carp and not normal carp Cyprinus carpio as these could have large negative affects on other pond life!

But if these lakes are not in your garden, but in 'the wild' you will need a licence to stock them with Grass Carp. See eFishBusiness - Controls on Non Native Fish Species for further information.

henrya