Gardening Matters

I wonder if you have noticed a significant increase in the number of homes sporting signs to indicate that they are using a mosquito program to rid their yards of these pesky nuisances. These yard signs seem to be popping up everywhere. Concerns about the rare but possibly deadly effects of West Nile virus or Dengue fever are certainly something to consider. And some people do suffer terrible reactions to even a simple mosquito bite. This has led me to do a little research on the effectiveness and safety of such bug services.

The following scientific information comes to us from the blog, TheGreenGrok, by Dr. Bill Chameides, the former Dean of the Department of Environmental Studies at Duke University.

There seem to be two types of these services; a topical spray that is refreshed every 3-4 weeks and a misting system that, like an irrigation system, sprays several times a day. Both systems use a combination of essentially the same chemicals:

Pyrethrum: This is a naturally occurring poison derived from chrysanthemum flowers. It is generally considered to be somewhat less toxic and less persistent in the environment. It is also less effective than its chemical cousins.

Bifenthrin: This is a synthetic poison which is considered less toxic than DEET and has the lowest EPA caution rating. However, it is highly toxic to fish and aquatic organisms as well as bees. Bifenthrin is also relatively persistent in the environment and may have additional toxic effects. This chemical is used in monthly topical spray programs.

Permethrin: This is one of the synthetic cousins of pyrethrum. The label for permethrin notes that EPA has classified it as “likely to be carcinogenic to humans.”

Piperonyl butoxide (PBO): This is a chemical “booster” that works alongside of Bifenthrin or Permethrin to increase their effectiveness. It is listed by the EPA as a possible human carcinogen.

There are also “green” mosquito repellant programs that are periodically applied by spray. Typically these will use a spray of oils from herbs like rosemary and spearmint which are supposed to drive mosquitoes away. They are considered much safer and user friendly to humans and the environment than the sprays noted above. They sure do make your yard smell good for a while in any case. However, according to a friend who switched from killer chemicals to a “green” repellant approach, the sprays seem to be rather less effective.

The fact that all of these chemicals are approved by the Environmental Protection Agency is to be taken with a tall drink of caveat emptor. EPA approval means that so far there is not enough compelling evidence to prove that these chemicals are in fact sufficiently dangerous to humans, animals and the environment to warrant banning them or severely limiting their use.

The tried and true alternative to all of this is to eliminate standing water and use fans to blow the wee beasties away. When this is not possible, consider a screened-in deck, porch or patio.

Consumers will need to weigh their concerns about mosquito bites against the cost and consequences of chemically based mosquito controls. Such consequences include those not just for yourself and your family, but also for neighbors and the general environment.

Hopefully this column will give you something to think about as you consider a mosquito control program.

Jeff Coghill has been gardening in DeKalb County for over 35 years. He has killed at least one of every plant he has tried before getting another to thrive. He is a volunteer at the Dunwoody Nature Center and works closely with the Master Gardeners there.

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