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Botanical pesticides safer than synthetics? Not necessarily BOTANICAL vs. SYNTHETIC

October 5, 2012 12:10 am


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Guy J. Mussey is an agent in Virginia Cooperative Extension's Stafford County office, specializing in environmental horticulture. Phone 540/658-8000; fax 540/658-8006; email

IN MY LAST article I tried to tackle a couple of common gardening myths, and promised that in subsequent articles I would continue to set the record straight when it comes to garden misconceptions.

But before I do that, let me say once more that many myths are handed down orally with no scientific basis to them. Occasionally a myth is actually proven through rigorous scientific research; however, most are not.

If you are interested in doing your own myth/fact research, a good place to start is a book titled "The Informed Gardener" by Dr. Linda Chalker-Scott. Chalker-Scott is the extension urban horticulturist at the Puyallup Research and Extension Center of Washington State University. She has dedicated her career to searching the scientific data in an effort to find the truth. Her work is the basis for much of what I'll be writing about.

The myth I'll challenge in this article is the one that botanically derived pesticides (botanicals) are safer than synthetics.

It has long been known that plants can produce substances that can deter or even kill insects and other herbivores.

Some botanicals cause allergic reactions in people, others are highly toxic to fish and animals, and some may even cause cancer.

Some common botanical pesticides are nicotine, derived from the leaves of the tobacco plant; pyrethrin, derived from the pyrethrum daisy; rotenone, derived from the roots of more than 68 plant species; ryania, a mixture of compounds extracted from the roots and stems of the tropical plant Ryania speciosa; sabadilla, derived from the seeds of South American lilies; and neem, derived from the neem tree that grows in arid tropical regions.

Nicotine is a highly neurotoxic chemical with an LD50 of 55. LD stands for "lethal dose"; LD50 is the amount of a material, given all at once, that causes the death of 50 percent of a group of test animals. The LD50 is one way to measure the short-term poisoning potential (acute toxicity) of a material.

Essentially, the lower the LD50, the more toxic the substance. See the accompanying chart, which gives a comparison of the toxicity of these botanicals and a couple of synthetic pesticides.

Botanical insecticides can be as toxic as, and in some cases more toxic than, synthetic insecticides. Use of these materials should not be taken lightly. We should be cautious in the use of any pesticide.

To put this in perspective, aspirin has an LD50 of 1,200; table salt's is 3,320; and caffeine's is 192.

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