Although it would be a good idea to call your county extension office first, copper sulfate is used to treat stock water containers for algae. I would think it would be safe to use on the pasture, too. We have had this same thing in a small area of our lime-rock driveway and it is nasty and slippery. I sprayed it with bleach water but of course you wouldn't be able to use that.

Do not use cooper on the soil. It builds up heavy metals in the soil. Bayer makes a Moss and algae killer you can spray on it. Be sure to read the directions carefully.
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Thank you for the responses. I will look into the copper to see if that is a possibility but sounds like it won't be. I googled bayer m&a killer and it got pretty poor reviews, but I will try it anyway.

If anyone else has suggestions, please share. I am thinking mowing it would be bad...right? what about pouring salt on it?? Like kosher salt or rock salt? I mean, it would take a whole lotta salt....

Hi again! I called Bayer to make sure it is safe for horses to graze. He had to send my inquiry to some other department. he said it may be 2-3 days before I get my answer, but he is guessing 14-30 days. i had told myself that whatever number they gave me, I would wait some extra time, but to wait over a month is really not possible (well, i mean, I can't turn them out with the algae in the pasture, so of course it *IS* possible...i am just kind of frustrated right now!)

I just am questioning the safety. I am really bummed and would love any other suggestions. Thanks!

Did you try contacting your local extension office?? They deal a lot with farmers and ranchers and should know what the safest, easiest solution would be. There is a lot of stuff on the web on the danger and toxicity of ingestion of certain algae by livestock. So I don't blame you for being desperate for a solution quickly.

yes, I will. Good idea. Thanks for that suggestion, although I am reading this in Saturday, and Monday is Columbus Day. I finally heard back from Bayer, they said the pasture would be safe 24 hours after spraying. I am still a little (a lot)paranoid though.

We have had cooler, drier weather for a few days now. Most of the Nostoc is black and dried up/crunchy underfoot. I tried to rake it up but it just breaks up, plus takes forever. I am wondering if dried Nostoc is no longer "living" and therefore safe...or maybe it now has concentrated properties and is *worse??* I may start a new thread asking about that.

The weather is so pretty and I would love to see the horses out there, enjoying it!

FYI, the horses are NOT stalled, they have stalls attached to large shady paddocks and can go in and out at will. If all I had were stalls I would be borrowing a friends' pasture to make sure they got out to graze and stretch their legs. I just want to make that clear.

gosh, this thread makes it sounds like it would be GOOD for horses. I don't know what to make of all this information. I called my vet about it when i first saw it...she said to keep the horses off the pasture...but sometimes I wonder if they advise that "just in case?" I don't want to be an idiot and not listen to the vet, but then again, if she is just making sure nothing comes back to bite her in the butt and she is not SURE it is bad for horses...then I want to continue researching.

Here is a link that might be useful: thread about nostoc and horses

I've got it growing all over my crushed shell drive. I've raked it up, but it just comes back. I sprayed it with a bleach solution, and that seemed to dry it up a little, but not much. Someone suggested sprinkling it with boraxo. I didn't try that as I have dogs and didn't want it getting on their feet. We haven't had rain for a few days now and it it starting to dry up.

Thanks for the quick reply, echobelly! I guess I cannot use either things you mentioned due to the horses, correct? Have you tried the Bayer Moss and Algae killer?

I am also trying to confirm whether Nostoc Commune is bad for horses or safe. If it is safe, then I am fine to turn them out with the algae still out there.

Just a thought. How big is the field? Is this growing over the grass or smothering it? If it's some scary stuff, would it be worth it to just scrape the whole danged thing with a bobcat and reseed?

I changed our grasses where the animals are from Bahia to Bermuda as bermuda helps dysentery, thus actually giving animals something worthwhile when they go seeking grass for digestion, cats, dogs, crazy pony that escapes from her farm a half mile away and stands at my gate waiting to play with my dog, who's danged near big as that pony, lol.

I don't know much about it, but if it's going to be like a spore thing that never goes away without removing the topsoil, would scraping it down and starting over the winter help? Just a thought.

We suffered for years with nostoc on our driveway. We tried every weed killer we could find, copper sulfate, lime, buring it off and even spray painting it (we were desperate). Someone recommended baking soda so we tried it on a small patch and it WORKED! The stuffed turned brown after a few days to a week (we have found brown is the dead color - black is the just waiting for more water color). We then bought big bags of bicarbonate of soda from the local feed store and spread it on the driveway using a drop spreader. It is working!!! We will play with concentrations of dissolving it in water and spraying once the major "kill" is done - but we would highly recommend trying it.

Baking soda will kill crabgrass, too. Much cheaper than RoundUp.

Borax shouldn't hurt the dogs. I put it on my yard every year for fleas, and my cats were fine. Actually, I take 1/8 tsp of borax every day. It's not any more toxic than table salt.