Lewis Creek Farm
Key to Specific Pesticides
See "What is LD50" for a detailed explanation of LD50,
but in short, a higher number means less toxic

B.t. (Bacillus thuringiensis) LD50>5000 mg/kg
B.t. is a naturally occurring soil bacteria. Different strains of it attack different insects, and are highly specific. For example, the strain that attacks cabbage "worms" is actually attacking cabbage caterpillars, not worms. It only attacks true caterpillars, not centipedes, not earth worms, only caterpillars. Similarly the strain that attacks Colorado Potato Beetles is very specific to beetles like the Colorado because, in fact, it only attacks them in the young soft bodied stages. The very specific nature of B.t. makes it very safe for humans and hence it is approved for organic production.

Synthetic Pyrethroid LD50=2305 mg/kg
Pyrethrin is an insecticide derived from the Chrysanthemum plant. It is very toxic to insects, but only mildly toxic to humans. Because it is naturally occurring and only mildly toxic to humans, it is approved for organic production. Synthetic pyrethroids, are man-made chemicals that are similar to pyrethrin and like naturally occurring pyrethrin, are very mildly toxic to humans. However, because they are synthetically produced rather than naturally occurring, they are not approved for organic production.

Surround LD50=Non-toxic
Surround is made entirely of kaolin clay. Just plain old clay. When it is diluted in water and sprayed on plant leaves it leaves them with a milky residue that makes the leaves a very undesireable meal to insects. It does not kill anything, and is not poisonous in any way, but rather deters the insects.

Cupric hydroxide LD50=1623 mg/kg
Cupric hydroxide is a very simple copper compound. Copper is a necessary plant nutrient. When applied in this form to plant leaves, it kills fungus spores when they land on the plant and prevent the fungus from getting a foothold. It is approved for organic production.

Linuron LD50=4833 mg/kg
Linuron is a synthetic herbicide. We use it to control weeds in carrots and parsley. We apply it very early in the season, at least 2 months before harvest begins.

Malathion LD50=3946 mg/kg
Malathion is a synthetic insecticide. We use it to control Tarnished Plant Bugs (TPB) in strawberries. It is applied to the strawberry plants just as the blossoms are starting to open, about a month before the strawberries are ripe. The strawberries themselves never get sprayed.

Atrazine LD50=1886 mg/kg
We have a long history of raising sweet corn with no sprays at all, however, very rarely we need to save a planting of sweet corn from the weeds. When this happens it is only a very small portion of the year’s crop that receives an application of Atrazine. Most "Cow Corn" you see is sprayed with Atrazine.