How Organic Insecticides Work

When crop rotation and other methods don't work, some organic farmers turn to organic insecticides to save their crops. See more green science pictures.
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If you're not a serious devotee of organic foods, you might assume that the words "organic" and "insecticide" are mutually exclusive. But guess again. Even farmers who earn the U.S. Department of Agriculture's certified organic label, which requires them to adhere to a regimen of environmentally sustainable and health-conscious methods, are allowed some wiggle room to use certain synthetic chemicals and pesticides to control bugs, weeds and plant diseases. Basically, the exception kicks in when the preferred non-chemical methods, such as insect traps, crop rotation and hand-weeding, aren't sufficient to protect crops from destruction [source: USDA]. That said, the permitted artificial helpers usually aren't heavy-duty bug killers of the DDT ilk. Most of them are relatively mild substances. For example, take potassium bicarbonate. It's a manufactured chemical that's an effective fungicide against powdery mildew, but it doesn't cause any apparent long-term health problems for humans (even though it can interfere with reproduction in mice) [source: FDA].

Even so, a lot of hardcore organic farmers -- and do-it-yourself organic gardeners as well -- wouldn't even think of using anything artificial on their precious fruits and vegetables. Instead, if they feel the need to use a pesticide (or an insecticide, which is simply a type of pesticide that targets bugs), they turn to an assortment of natural substances. Some are gleaned from exotic foreign plants. For example, sabadilla is a bug repellant made from seeds of a South American lily, and Ryania, an antidote to European corn borers and harmful worms, is concocted from the ground stems and roots of a South American shrub. They also utilize more commonplace substances, such as a puree made from cornstarch and crushed tomato leaves -- it contains solanine, a chemical that has an inhibiting effect on black spot fungus [source: Abraham].


But are these organic bug and fungus fighters really effective? And more importantly, are they even safe? First, let's delve into the various types of organic insecticides.

Types of Organic Insecticides

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An organic citris farm in California attempts to protect its crops from harmful chemicals.
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You might assume that insecticides are a recent development. But in truth, farmers have been using various substances to keep pests from ravaging their crops for thousands of years. In 2500 B.C., the Sumerians used sulfur to kill insects, and over the centuries, farmers in various parts of the world tried other sorts of chemical insecticides as well -- even substances like arsenic and lead that are highly dangerous to humans. Believe it or not, in the 1940s, the introduction of synthetic chemical insecticides was seen as a cure-all that would eradicate pests for good. But the pests proved remarkably resilient, and the powerful chemicals sometimes harmed other benign species and even people [source: McKinney, Schloch and Yonavjak]. That led many folks to reconsider older, less harsh methods -- and to try new substances gleaned from plants and soil in other parts of the world.

Basically, there are two broad classes of pesticides that can be used in organic farming, according to USDA regulations. In the first category are substances that are synthetic compounds not generally found in nature, but which have been deemed by scientists to be safe and non-threatening to both food consumers and the environment. These pesticides usually are simple compounds that include naturally occurring substances like copper or sulfur [source: Langois].


In the second category are naturally occurring substances, many of which are extracted from plants or from the earth itself [source: Langois]. One such organic pesticide is spinosad, which is produced by Saccharopolyspora spinosa, a rare species of bacteria that was found in soil samples from a Caribbean island in 1982. The bacteria basically act as tiny pesticide manufacturers, fermenting the soil and producing spinosad, which gives the soil a sweet, healthy aroma. But that smell can be deceptive -- at least if you're, say, a Colorado potato beetle or a caterpillar. When those bugs ingest spinosad, either by coming into direct contact with it or by eating a leaf sprayed with the chemical, it acts as a potent nerve poison. The creatures lose control of their muscles and helplessly die. While that grisly fate may seem a little, well, disturbing to some folks concerned with being kind to the Earth, it's important to remember that if those tiny freeloaders gobble up your vegetables, you're not going to have anything to put in your vegan stew. On the plus side, scientists have found that spinosad has very low toxicity in mammals, including humans, and that it doesn't seem to cause cancer or nervous system damage [source: Cornell University].

OK, so we understand where organic pesticides come from and how they work. But are they really better than the non-organic version, or at the least safer?


The Effectiveness of Organic Insecticides

A pile of washed organic carrots waits to be refrigerated at the Clear Brook Organic Farm in Vermont.
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In most people's minds, the word "organic" is synonymous with words like "natural," "healthy" and "safe." And it's certainly appealing to think that something labeled "organic" works as well as or better than an artificial chemical concoction. But unfortunately that's not always the reality.

For one thing, some natural insecticides actually are very similar to synthetic ones produced in laboratories. One example is the potent natural poison pyrethrum, which is derived from the powered, dried flower heads of the pyrethrum daisy native to southwest Asia. Pyrethrum is very similar in structure to a class of synthetic insecticides called pyrethroids -- but unlike them, it's approved for use in organic cultivation. Pyrethrum is a fast-acting poison that disrupts insects' nervous systems and causes paralysis. In small quantities, pyrethrum may not be sufficiently potent to kill a bug, but when combined with other substances, such as nutmeg oil, it becomes much more effective. But how safe is it? The powder is relatively non-toxic for humans unless swallowed in substantial quantities. And it breaks down rapidly when exposed to the elements, so there's little chance of a buildup in food or water. But pyrethrum does have downsides; it's a hazard to fish like bluegill and lake trout, which is why organic farmers are encouraged to try other pest-control methods first before resorting to using it [source: Cornell University].


But organic pesticides are still better than those old, harsh chemicals, right? Maybe, maybe not. In a 2010 study published in the online scientific journal PLos One, Canadian environmental and agricultural researchers compared the effectiveness and environmental impact of organic-approved pesticides with synthetic ones in thwarting soybean-eating aphids. They found that the organic pesticides had a similar or even greater harmful effect on other species and the overall environment, in part because much larger doses of the organic pesticides were required to get the job done. "These data bring into caution the widely held assumption that organic pesticides are more environmentally benign than synthetic ones," they concluded. They recommend that, instead of focusing on whether a particular chemical is natural or synthetic, organic farmers should be allowed to assess all pesticides for their impacts before making a selection [source: Bahlai].

It's also important to remember that insecticides aren't the only way to protect crops from pests. Other non-chemical methods, such as crop rotation, not only have a history of decreasing damage from insects, but protect the soil's fertility as well [source: Peel]. So, if you're planning to grow organic foods, you might want to consider those methods first, and rely on insecticides as a last resort.


Lots More Information

Related Articles

  • Abraham, Katy and Doc. "Guide to Organic Pesticides." Mother Earth News. February/March 1994. (March 29, 2012)
  • Bahlai C.A.;, Xue Y; McCreary C.M.;, Schaafsma A.W.; and, Hallett R.H. "Choosing Organic Pesticides over Synthetic Pesticides May Not Effectively Mitigate Environmental Risk in Soybeans." PLoS ONE . 2010. (March 31, 2012)
  • Delate, Kathleen. "What is Organic Agriculture?" (March 31, 2012)
  • "Material Fact Sheet: Pyretheum." (March 31, 2012)
  • "Material Fact Sheet: Spinosad." (March 31, 2012)
  • McKinney, Michael L.; Schoch, Robert M.; and Yonavjak, Logan. "Environmental Science: Systems and Solutions." Jones and Bartlett. 2007. (March 31, 2012)
  • "The National List of Allowed and Prohibited Substances." March 29, 2012. (March 29, 2012)
  • "Organic Production and Handling Requirements." March 29, 2012. (March 29, 2012)
  • Peel, Michael D. "Crop Rotations for Increased Fertility." January 1998. (March 31, 2012)
  • "Potassium bicarbonate." Oct. 31, 2006. (March 29, 2012)