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Keeping rain barrels mosquito free

I have two different style (commercially made) rain barrels which I
use primarily for watering my vegetable garden. It has become very apparent that the screening on top is not enough to keep mosquitos from breeding.

I did a little searching and goldfish were recommended. I think this would be a dismal existance for a fish and don't even want to think about the water getting low, winter coming, etc.

I do not want to use chemicals since I garden organically.

At this point I have poured several cups of vegetable oil in each with the hope that it will float on top and inhibit the mosquitos. So far it has seemed to be working.

Any thoughts or advice?

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  1. I've only heard of fish for this use. I don't believe they have highly developed enough brains to experience a "dismal existence." But then who's asked them?

    1. If you put in fish, wouldn't you need some oxygenating plants? When I had small pond some inexpensive parrot's feather and a few goldfish kept the water free of mosquitoes. The raccoons did eat the fish from time to time. It seems like more trouble than it's worth for a rain barrel.

      1. Why can't you simply cover them with heavy plastic when it's not raining?

        1. I think we have the same rain barrel as you do, with the screen. It was my second barrel. After the first season it I never used it again. The first rain barrel I bought 20 years ago is still in use and has no problem with mosquitoes. It's the Great American Rain Barrel, and they recommend draping a Teflon window screen over top of the barrel before screwing on the cover. However, if you have the barrel I think you do, the screen merely sits in a groove on the top. Still, I think an additional screen on top of that one would prevent insects from getting into the water. You could place small rocks around the perimeter of the screen to hold it down. I think you don't want fish in that barrel. It will smell very bad in no time at all.

          Here's the GARB site:

          1. You'll want to use Mosquito Dunks. We've been using them for years in our rain barrels (which we use to water our organic gardens). They are made of Bt, a bacteria that will kill mosqito larvae---and harm nothing else! I drop a small piece of these "donuts" in each rain barrel every few weeks or so. You should be able to find them at your local garden center. If not, find them here: http://www.amazon.com/gp/product/B000...
            The same company makes it in another form---tiny nuggets sold in a shaker-top cannister. I've used both and they work equally well.

            1 Reply
            1. re: Anne

              This sounds like the ticket!

              Thank you.

            2. Without seeing a picture of your rain barrel, I'm having a hard time imagining how mosquitoes are getting past a piece of screening. Is there an unscreened opening that you could cover? Would augmenting the factory-installed screening with some nylon window screen material help?

              We have several improvised rainwater catchments (a.k.a. trash cans) in our yard, and the window screen works like a charm at keeping the mosquitoes at bay.

              I'm not questioning the efficacy of the dunks, but I guess if I were in your shoes, I'd rather use a one-time fix rather than a fix that requires repeated applications.

              5 Replies
              1. re: hohokam

                There is no visible compromise to the screens. All openings are secure. We are in the South just adjacent to a marshy greenway, so it is already extremely buggy. We realized the rain barrels were contributing to the problem when we recently moved them in order to raise the height of the faucet to better accommodate the watering can.

                I read that the larva can be washed into the barrels. Perhaps at some point after hatching they are small enough to pass? Beats me, all I know is when the barrel is fairly empty and it is bumped swarms arise and attack!

                1. re: meatn3

                  Do you have West Nile Virus where you live? When I used to have horses I read that the mosquitoes can breed in water in a hoof print. Not something to risk, for sure.

                  1. re: c oliver

                    We do, since 2002.

                    I once lived in Fl. and remember an article in the St. Petersburg Times about mosquito control finding them breeding in the bedside glass of water a man used to soak his fake teeth nightly.

                    1. re: c oliver

                      Even small amounts of debris in gutters or gutters that are pitched inadequately can cause pools that may permit mosquitoes to breed. The type that carries West Nile virus is particularly capable of producing larvae in small quantities of water while the so-called flood-water mosquitoes can produce in pretty small amounts of water. A good rain after a period with small amounts of water in the gutter could flush eggs or young larvae into the rain barrel. You would pretty much have to filter the water coming down the downspout to keep eggs out. I do not know how you could get sufficient filtering for eggs while still allowing an adequate flow to handle a thunderstorm.

                      1. re: Eldon Kreider

                        Yes, in my locale I think the mosquito dunks will be the best solution.