Pyrethrins Pyrethrins are refined from natural pyrethrum, which is extracted from a species of chrysanthemum. These chemicals provide quick knock-down, but their residual activity is brief, so they must be applied often if insects persist. Pyrethrins are effective against most garden pests, especially soft-bodied forms, since the killing action is by absorption through the skin. They are not effective against spider mites. Rotenone Most rotenone is produced from roots of the derris plant that grows in South America.
Rotenone is the most effective and readily available of the non-synthetic insecticides.
It is effective for most garden insects, but not for spider mites. The residual activity is very short. Sulfur Finely-ground sulfur can be used as either a dust or a spray. Sulfur also may cause an unpleasant taste if used on vegetables shortly before harvest. Insecticidal Soaps Recent research indicates that certain detergents or soaps can effectively reduce populations of certain soft bodied pests such as aphids, mites, leafhoppers, plant bugs, and thrips.