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Mosquito Control 101

Q. I need mosquito control tips! I remember hearing a guest on your program suggest introducing frogs to reduce the mosquito population, but I'm worried that anything I do to introduce frogs will also introduce more mosquitoes! Thank you! -
    ---Karen in Harvard, Massachusetts
A. Ah, yes—the fabled 'haze of memory' strikes again! Unfortunately, that's not what you heard back then Karen, because these amazing amphibians don't control mosquitoes or mosquito larvae. Adult frogs (and my favorite beneficial creatures, toads) emerge from hibernation in the Spring, mate and lay their eggs in water—especially vernal ponds and pools; those ephemeral bodies of water that dry up in the summer. But the tadpoles that hatch from those eggs only eat plant material and algae. The adult frogs and toads that the tadpoles morph into DO eat lots of pests—including slugs, snails, cutworms, earwigs, and cuke, squash, bean and other bad beetles—but not mosquitoes.

And because mosquitoes will gladly breed in the same water as these fine creatures, we always urge folks to treat ponds, water gardens and vernal pools with BTI—the form of Bt that prevents biting insects like mosquitoes, blackflies, and gnats from breeding. A naturally occurring soil organism, BTI is completely safe for people, pets, birds, wallabies and anything else that isn't a nasty bloodsucker.

You've all seen the small, doughnut-shaped BTI 'dunks' sold for this purpose. I prefer the granulated form; it's easier to use to treat small, wet areas. Apply a fresh run of BTI to ponds and other season-long water sources once a month and you'll keep the local mosquito population to a minimum.

(Having mosquito-eating fish in a pond will also keep mosquitoes from breeding, but those fish are also going to eat a lot of frog and toad eggs and tadpoles. So if possible, use BTI and keep fish out of water gardens and the like early in the Spring, when most amphibian breeding takes place.)

Q. Hey Garden-guy! Is there anything I can use in a small stagnant fishpond to safely eliminate mosquito larvae? (There are raccoons and cats in the neighborhood that drink from the pond.) I plan on digging it out, but in the meantime it's the perfect mosquito breeding ground because there's no pump to keep the water moving. Thank you ever so!
    ---Jennifer in Memphis, TN
A. You want to be nice to raccoons? You may enjoy looking at those cute little bags of rabies, but it is not wise to encourage them; they can be mean, they get surprisingly big and cause all kinds of trouble. That said, it sounds like that your fishpond must be fish-free. Good. Leave it that way, treat it with some BTI and let frogs and toads breed in it.

Your point about moving water is well taken; having a fountain or waterfall or some other way of keeping water moving can be very helpful at preventing mosquitoes from breeding—and it doesn't deter frog and toad production one bit!

Q. Mike: The mosquitoes in our yard are around all the time, not just in the evening like the old days. They really seem to like the black eyed Susans that surround our deck, which I have to reach through to water our Earth Boxes, where we grow a lot of our vegetables (tree roots limit our in-ground space). Do you think they're breeding in the Earth Boxes? Do black eyed Susans attract mosquitoes? Is there anything that can get us back outdoors? Thanks, I love the show—and when you edited O.G.
    ---Jenny in Cherry Hill, NJ
A. Well, thank YOU, Jenny! My guess is that 'Susan' is largely innocent; your mosquitoes probably just enjoy the dense shade she provides during the heat of the day. The Earth Boxes are another story. Mosquitoes need water to breed, and those containers seem to always hold a lot of liquid. (I've seen tomato plants totally rotted out by their lack of drainage.) I recommend you switch to 'real' containers; big pots with good drainage that you'll fill with ¾ of a nice, light, loose potting mix and ¼ compost.

And be sure to do a Springtime check of all standing water on your property. You know the drill: Empty out buckets and wheelbarrows, look for cat food cans that fell out of the recycling, rinse out birdbaths once a week…

…and clean out your gutters! Female mosquitoes stay close to where they were born, because they'll need that standing water to lay THEIR eggs in after they suck your blood. You can break that nasty cycle by getting rid of their childhood water; and gutters are the biggest unseen source. I finally took my own advice on this several years ago and found hordes of mosquitoes having wild sex parties up there! I drained the gutters and had almost zero mosquito problems that year.

If the problem persists, try one of the garlic sprays sold for mosquito control. Great for outdoor parties in the summertime, these sprays are said to keep an area free of all kinds of bloodsuckers for at least two weeks—up to six weeks if rain is scarce. And they couldn't be safer for people; their only active ingredient is garlic oil. (Mosquitoes ARE vampires!) Ask for them at retail stores or search the Web.

And keep a DEET-free mosquito repellant on hand. The original "Bite Blocker" (soybean and coconut oils plus essence of geranium) has been shown to work as well as some concentrations of DEET in highly regarded medical studies, including one published in the New England Journal of Medicine. (Those compulsive product re-namers at Gardens Alive sell this original formula under the " Sting Free" brand name.)

And this summer, a new Bite Blocker product whose progress we've been following for several years will become available. Dubbed "BioUD" (the nickname for the active ingredient, undecanone—a component of primitive wild tomatoes and rue plants), this new repellant was developed by Dr. Michael Roe, a William Neal Reynolds Distinguished Professor of Entomology at North Carolina State University. It received full federal EPA approval for mosquito and tick control on March 15th of this year, and will be available across the country as each individual state approves its labeling. You can chart the progress at their website:

For more detailed info about mosquitoes and repellants, including some of the reasons you should stay away from DEET, check out these PREVIOUS QUESTIONS OF THE WEEK Insect Repellants—Plants and Products You Can Use This Summer; and New Alternatives on the Way and Turn a Triple Play Against Nasty Mosquitoes .

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