Canadian Pond weed (elodea) control

I have a pond about 20 metres by 6 meters and around 0.6 m deep. One dark day several years ago my wide decided some pond weed would be a good idea (it wasn't). The plant in question - elodea - is now utterly rampant and the pond is overwhelmed.

My question is therefore how best to remove it or at least control it ?

I have tried two basic strategies:

- mechanical raking. The best intrument I have improvised is a old scythe with a 20 ft rope for retrieval. If I chuck it in a drag it I can slowly rip the elodea out complete with roots. This does at least work, but its back breaking work and slow. I did "a bit" last night and have twenty wheel barrows full of weed. It is really no fun at all, especially as the mud is an evil slimy grey. There are a lot of bull rushes etc too that get in the way, so you either take them out or leave bits of elodea - neither being satisfactory. There are also times of year when I can't really do this - spring say is full of frog spawn.

- weed killer. Last year after an epic raking section I drained all but 6" of water and sprayed the remaining elodea with roundup. This was relatively easy to do, but did not last. Maybe I was too timid with the dose. The fish didn't mind at all fortunately (roundup is supposed to be aquatic life safe). I also don't want to kill every plant just the elodea.

Things I haven't tried:

- grass carp. I would rather not add another alien life form unless a last resort and likely to work. Elodea is at the woody end of water plants, is this grass carp food ?

- any purpose made weed cutter/removers that might make mechanical raking more practical.

- more serious forms of weedkillers/higher doses of the same stuff (roundup).

- putting down black plastic sheets at the bottom of the pond, so plants cannot root. It would be fine if the elodea were just in the edges with the middle of the pond clear.

- adding shade. The site is sunny. I doubt I could engineer full shade though.

- introducing an even more vigourous species to out compete the elodea. Water lillies say would look a lot better. What species might be good choices ?

I would appreciate any advice on my problem !

Mike

 

"roundup is supposed to be aquatic life safe"

My understanding is that whilst Roundup is generally very safe (attacking an enzyme that only exists in plants, not in animals) it can cause damage to aquatic animals:

http://en.wikipedia.org/wiki/Roundup#Aquatic_effects

but the Monsanto site does talk about a Roundup Pro Biactive formulation that has better efficacy than previous formulations, and is less harmful to aquatic life - but then that's their marketing site, so "they would say that, wouldn't they"

http://www.monsanto-ag.co.uk/layout/industrial/aquatic.asp

 

It was the Pro Biactive I used.

 

Hyco. elodea is an excellent oxygenating plant and no doubt gives your fish shelter and is part of the natural cycle, if it were me I would go for the grass carp option as a way of controlling it, they will eat it it's not too woody for them.

 

Roundup is aproved for use on aquatic plants and is reasnably effective, however i tend to agree with wallnut.

As with all pesticides and herbicides, you should follow the instructions as per dose, The manufacture's carefully calculate the dose rate and doubling the dose is usually inefective better to make a second spraying a week or so later.