Lewis Creek Farm
What is LD50?
The inverse measure of pesticide toxicity

LD50 is the standard measure of pesticide toxicity. The higher the number, the less
toxic the pesticide. Hereís why: All pesticides, even those approved for organic production, are tested in the following manner. The pesticide is fed to mammalian test subjects (probably lab rats) in increasing doses, until half of the subjects die. This dose is the lethal dose that killed 50% of the mammalian population, or LD
50. It is measured in milligrams of pesticide per kilogram of body weight, or mg/kg. So the higher the LD50 the larger the dose it took to kill 50% of the mammalian population and therefore the less toxic the pesticide.

Note from the LD
50s that even the pesticides approved for organic production are toxic at some level, except for Surround, which is plain old clay. Note as well that some of the synthetic chemicals we use are less toxic than some of the pesticides approved for organic production. For example Cupric Hydroxide (approved for organic production) has a lower LD50 (that means itís more toxic) than either Malathion or Linuron, which are not approved for organic production.

Another interesting fact about pyrethrin and synthetic pyrethroids:
The synthetic pyrethroids have an LD
50 of 2305 mg/kg and the naturally occurring pyrethrins that are approved for organic production have an LD50 of 1500mg/kg. Lower LD50 means more toxicity. So, the natural pyrethrin which is approved for organic production is more toxic than the synthetic pyrethroid which is not approved for organic production.

Now that you know what LD
50 means, it mat prove interesting to compare the toxicity of various commonly used pesticides.