by Craig Weatherby
The ad shown at left, from the June 30, 1947 issue of Time magazine, became an anachronistic artifact after publication of Rachel Carson's Silent Spring, which documented the eco- and human health dangers of DDT.
While DDT has been banned in the U.S. and most developed countries, it remains a critical ally against malaria in many afflicted countries, where public health experts defend limited household use as the lesser of two evils.
But few believe that it's wise to use potently toxic synthetic pesticides unless they're proven essential to save lives or feed hungry people... especially when effective alternatives are available.
(This, among other reasons, is why we favor organically grown fare over conventional crops.)
Fortunately, new evidence review indicates that extracts from common kitchen seasonings—and plant essences used in aromatherapy—could become a serious alternative ally against insect pests.
Plant extracts as safer preservatives and pesticides
It's well-proven that extracts of herbs like rosemary, oregano, and clove possess potent antibacterial powers against meat-spoilage and food-poisoning bacteria (Fu Y et al. 2007; López P et al. 2007; Burt S. 2004).
And in two presentations at the recent American Chemical Society National Meeting, scientists from Canada reported that their evidence review supports the practicality—within limits—of using herb and spice extracts as safe, eco-friendly alternatives to conventional petrochemical pesticides (Isman MB 2009).
“We are exploring the potential use of natural pesticides based on plant essential oils—commonly used in foods and beverages as flavorings,” said study presenter Murray Isman, Ph.D., of the University of British Columbia (Sampson MT 2009).
(Rather than fats, the constituents of the misnamed extracts called “essential oils” are pungent, non-oily compounds such as ketones and aldehydes.)
The new pesticides blend tiny amounts of two to four different spice extracts, diluted in water. Some kill insects outright, while others repel them.
Over the past decade, Isman and his colleagues have tested many plant essential oils and found that they attack a broad range of agricultural pests.
Some spiced-based commercial products now being used by farmers have already shown success in protecting organic strawberry, s
pinach, and tomato crops against aphids and mites.
“These products expand the limited arsenal of organic growers to combat pests,” explains Isman. “They're still only a small piece of the insecticide market, but they're growing and gaining momentum” (Sampson MT 2009).
The natural advantages
Unlike conventional pesticides, these are derived from foods already approved as safe, and are readily available.
And pests are less likely to evolve resistance to these natural toxins, thanks to the presence of diverse chemicals in each extract, versus the single molecule found in most synthetic pesticides.
In fact, plants produce these chemicals to protect themselves against insects, fungi, and bacteria.
They're also safer for farm workers, who are at high risk for pesticide exposure and injury.
The natural disadvantages
Since essential oils tend to evaporate quickly and degrade rapidly in sunlight, farmers need to apply the spice-based pesticides to crops more frequently than conventional pesticides. Some last only a few hours, compared to days or even months for conventional pesticides.
The greatest promise is seen for first-world organic farms, and for farms in poor countries where regulatory burdens are lower.
Natural pesticides can be toxic. For example, rotenone is an approved plant-derived pesticide used on many organic farms, although it kills fish readily and can make people who ingest it sick.
But rotenone is much more toxic than most of the herb-spice extracts under review, which are short-lived and do not harm birds, mammals, or humans unless ingested in concentrations far higher than would be encountered on crops.
And these natural pesticides are generally less potent than conventional pesticides, so they also must be applied in higher concentrations.
Dr. Isman's team says that they and other researchers are seeking ways to make the natural pesticides stronger against insects, and more durable, to reduce the quantities needed and the number of applications.
“They're not a panacea for pest control,” cautions Isman. “But at the end of the day, it comes down to what's good for the environment and what's good for human health” (Sampson MT 2009).
Consumer uses for spice extracts
Some plant extracts show promise as eco-friendly home repellents against mosquitoes, flies, and roaches.
Unlike conventional bug sprays, which have a harsh odor, these natural pesticides tend to have a pleasant aroma, since many contain the same oils used in aromatherapy products, such as cinnamon and peppermint.
Manufacturers have already developed spice-based products that can repel ticks and fleas on dogs and cats without harming the animals.
Researchers are now exploring the use of other spice-based products - such as rosemary extract - for use on fruits and vegetables to destroy food poisoning microbes such as E. coli and Salmonella.
Other scientists are currently exploring the insect-fighting potential of lavender, basil, bergamot, patchouli oil, and at least a dozen other oils from exotic plant sources in China.
While funding for this study was provided by EcoSMART®, a botanical pesticide company, much of the research its authors reviewed was largely funded by government or non-commercial grants.
- Akhtar Y, Isman MB, Paduraru PM, Nagabandi S, Nair R, Plettner E. Screening of dialkoxybenzenes and disubstituted cyclopentene derivatives against the cabbage looper, Trichoplusia ni, for the discovery of new feeding and oviposition deterrents. J Agric Food Chem. 2007 Dec 12;55(25):10323-30. Epub 2007 Nov 20.
- Burt S. Essential oils: their antibacterial properties and potential applications in foods--a review. Int J Food Microbiol. 2004 Aug 1;94(3):223-53. Review.
- Fu Y, Zu Y, Chen L, Shi X, Wang Z, Sun S, Efferth T. Antimicrobial activity of clove and rosemary essential oils alone and in combination. Phytother Res. 2007 Oct;21(10):989-94.
- Isman MB. AGRO 24 Plant essential oils as repellents and/or deterrents to agricultural pests. Sunday, August 16, 2009. The 238th ACS National Meeting, Washington, DC. Accessed at http://oasys2.confex.com/acs/238nm/techprogram/P1287760.HTM
- Isman MB. AGRO 8 Opportunities for the use of plant essential oil-based insecticides in organic agriculture. Sunday, August 16, 2009. The 238th ACS National Meeting, Washington, DC. Accessed at http://oasys2.confex.com/acs/238nm/techprogram/P1287760.HTM
- Isman MB. Botanical insecticides, deterrents, and repellents in modern agriculture and an increasingly regulated world. Annu Rev Entomol. 2006;51:45-66. Review.
- Isman MB. Botanical insecticides: for richer, for poorer. Pest Manag Sci. 2008 Jan;64(1):8-11.
- López P, Sanchez C, Batlle R, Nerín C. Vapor-phase activities of cinnamon, thyme, and oregano essential oils and key constituents against foodborne microorganisms. J Agric Food Chem. 2007 May 30;55(11):4348-56. Epub 2007 May 8.
- Miresmailli S, Isman MB. Efficacy and persistence of rosemary oil as an acaricide against twospotted spider mite (Acari: Tetranychidae) on greenhouse tomato. J Econ Entomol. 2006 Dec;99(6):2015-23.
- Sampson MT. “Killer spices” provide eco-friendly pesticides for organic fruits and veggies. August 16, 2009. The American Chemical Society. Accessed at http://portal.acs.org/portal/PublicWebSite/pressroom/newsreleases/CNBP_022744