Questions on: Mosquitos

Ron Smith, Horticulturist, NDSU Extension Service


Q: I have a 10-gallon sprayer that I pull behind my lawn tractor and would like to spray for mosquitoes on a half acre of seeded grass. What would be the best type of insecticide to use and how much per 10 gallons of water? I have used Malathion in a 1 gallon sprayer. (Valley City, N.D.)

A: Malathion is certainly an acceptable mosquito control. I would suggest contacting vector control in Valley City to find out what they recommend using. The rate depends on the concentration of the product. That's why label instructions have to always be followed because there is no one formula.


Q: Is it possible to add something to the water in my rain barrels to prevent mosquitos from hatching out yet won't harm my plants? I considered the BT "doughnuts" they sell for ponds, but they are hard to find. I have put a couple goldfish in there in the past, but during dry spells the water gets too low and murky. With West Nile virus present in our area, I need to do something, but with the drought it is hard not to save every drop of rain that falls. Any ideas? (Howard S.D.)

A: In a rain barrel, a couple of tablespoons of vegetable cooking oil will do, and will not hurt your plants. The oil will float on the water's surface and suffocate the mosquito larvae. If that idea does not appeal, go to the nursery or garden supply store and see if they have a "summer horticulture oil." About the same thing and as effective.


Q. I have several rain barrels connected together with a drain at the bottom. They are open at the top, and I can draw water off from the bottom. What is the best way to control mosquitoes from breeding in the rain barrels? I have heard that putting oil on water keeps the larvae from being able to breath. What kind of oil can/should I use? Can I just put a couple of tablespoons of vegetable cooking oil in each barrel? Will this effectively control the mosquitoes from breeding in my barrels?

I want to be able to use the water for watering plants. I have heard of using oil like diesel fuel on ponds, but I don't want something toxic on my house, deck and garden plants. Will the cooking oil bother the plants? Especially if the water is just drawn off the bottom? What else is recommended? (Lisbon, N.D., e-mail)

A. There are several approaches I can suggest in your particular case. One, get a couple of goldfish for each barrel. The fish do an excellent job of keeping down mosquito larvae, plus they would provide trace amounts of fertilizer for your plants when you water. Be sure to rescue the fish before winter cold moves in.

Two, I would suggest using the "summer grade" of dormant oil (an oxymoron, actually). This is a light-weight oil that should disperse itself over the water surface and cause the larvae to suffocate. Or, as you suggested, a light-weight vegetable oil would do the same thing. The dilution rate would be so small that you need not worry about any possible toxic effects on plants, especially since you are taking the water from the bottom of the tank.


Q: I've seen "Lemon Grass" advertised for a mosquito repellent. Does it really work? Also, is it a perennial? (Davenport, N.D.)

A: The essential oil of lemongrass (Cymbopogon citratur) along with other citrus-scented lotions have a short-term repellent effect on mosquitos. The
plant itself does not, to any significant degree, have a repellent effect. It is annual up here, perennial in Texas, New Mexico and other such balmy places
(zones 7 to 9).


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