Invasive Duckweed?

[camo]

Hi

I visited a new to me site yesterday, Oughton Head in Hertfordshire is a spring fed wetland covering some grazed fields and a Reedy area. The reserve is a very pretty walk with good pathways that lead to the river source.

However my thread concerns the invasive plant that is fast clogging the water, I understand the plant was first noticed last year and it is already choking and blocking light to pats of the reserve. For those plant buffs out there can you tell me what plant is it and what methods of control are normally used for invasive duckweeds.

Roy

[ceterach]

Hi Roy

It is not a Duckweed, in fact it is a fern Azolla filiculoides. It is an alien and can cause considerable problems although in some cases these have proved only temporary (as in a few years). The only control I know of in large areas is careful herbicide spraying, clearly not very satisfactory.

It, like Duckweed can grow incredibly quickly. Thanks to people who throw garden plants out!!

All the best

John

[camo]

Hi John

Thank you for your clear information, I am not attached to the particular reserve but certainly I can guess the effect of control will be almost as severe as the plant.

Roy

[Jim Ford]

Huge areas of Crassula helmsii (New Zealand Pygmy Weed) took over the BBOWT reserve College Lake. I'm not sure how the altered water levels have affected it, but I suspect it'll be back.

Jim

[LindaB]

Hi

It can be controlled naturally by a little weevil. I will post more info later as I am at work and only just noticed this thread. All the info I have on this is at home.

The plant in the photo has a common name of fairy moss and as you have found out, is extremely invasive.

The little weevil used, is very effective. The weevil has no known ill-effects on our native species, and all stages of the weevil will only survive on this fairy moss. When the moss is gone, the weevil is also gone. I have seen it work for myself and is obviously much preferred to the insecticide route. They arent cheap to buy but they reproduce very quickly and are extremely effective.

When I provide you with further details later (hopefully), please get in touch with the warden for the reserve, as this moss will kill everything below the water level as it completely blocks out the light.

[Lancashire Lad]

Just seen this thread, and as ceterach & LindaB have said, current thinking has it that herbicidal/biological control is the best solution, as Azolla filiculoides (American water Fern) is incredibly invasive.

I would be surprised if the management team for the waterway concerned, are not already aware of the possibility for biological control, but the links below provide some useful information: -

(PDF File - Document size approx 200Kb) - http://www.nerc-wallingford.ac.uk/re...liculoides.pdf

(PDF File - Document size approx 2.75Mb) - http://www.invasivespeciesireland.co...%20control.pdf

(HTML Document - Document size approx 25Kb) - Newsroom - British Waterways

Regards
Mike.

[LindaB]

Originally Posted by Lancashire Lad

Just seen this thread, and as ceterach & LindaB have said, current thinking has it that herbicidal/biological control is the best solution, as Azolla filiculoides (American water Fern) is incredibly invasive.

I would be surprised if the management team for the waterway concerned, are not already aware of the possibility for biological control, but the links below provide some useful information: -

(PDF File - Document size approx 200Kb) - http://www.nerc-wallingford.ac.uk/re...liculoides.pdf

(PDF File - Document size approx 2.75Mb) - http://www.invasivespeciesireland.co...%20control.pdf

(HTML Document - Document size approx 25Kb) - Newsroom - British Waterways

Regards
Mike.

Well done Mike, you have posted most of the information I have at home. I have just one or two more links but the above links provide plenty of info on how to proceed. Some of this information is not easy to find on the internet either, it takes some searching lol.

There is a little pond near where I work that had a vast amount of money spent on it about 3 or 4 years ago for de-silting it by vacuum as its a sensitive area. It filled up nicely with rainwater (eventually) and all the wildlife started to return - and so did the idiots that dumped their ghost carp into the pond! I could see disturbance around the edge of the pond and eventually saw many carp appearing. I then started to see the fairy moss - which obviously came from the 'idiots' pond!

I was mortified when I saw it in there, knowing how serious this could be. Within a couple of months it rapidly took over - and I was on a mission! It was heartbreaking to see the newly hatched moorhens struggling to get through it and being a sitting target for any opportunistic bird. Some of the fish were struggling to get air during the summer months.

Cutting a long story short(ish lol), after researching and contacting various people, I came up with the above, and so did the local council responsible for the upkeep of the pond. I was fortunate enough to be there when these little weevils were being put in - they are very small indeed. A relatively small number were placed around the edge of the water and within a couple of months, very large areas of clear water appeared. I would say it took about 8 months to be almost completely clear with just bits around the edge, but the weevils obviously continued to work and it has been clear ever since. The speed in which the waterway clears is very much dependent on how many are added to the water initially (and how much they are prepared to pay).

Seeing this sort of thing is something I feel pretty strongly about and I do wish that this plant was banned from being sold (too late for those who already have it of course). I also feel that it should be compulsory to treat any waterway 'infected' with this stuff in the above manner, by whoever is responsible for the upkeep of it.

[camo]

Hi

Thank you all particularly Linda and Mike for the wealth of information I will certainly pass on the information to the Warden as I fear that the plant is fast taking over. I will also do my bit by watching out for any other infestations.

Hopefully I can let you know how the warden gets on.

Roy

[Mungo]

What a fascinating thread.
I have a pond within spitting distance from me and it gets choked with some kind of 'weed' in the summer months. I will look more carefully this year and see what kind it is.
Thanks for all the info.