• Medicinal plants have been used since ancient times to treat illness.Jupiterimages/Goodshoot/Getty Images
  
  In order to reduce the risk of cross-contamination of chemicals and other compounds, growers of medicinal plants often rely on organic methods of growing, including the use of biopesticides to control disease and infestation. The Environmental Protection Agency website defines biopesticides as specific types of pesticides that have been derived from organic material including animals, bacteria, minerals and plants.
  
  

Microbial Biopesticides

• Microbial biopesticides are those pesticides in which a microorganism is the main active ingredient. These microorganisms can include a species of bacteria, virus, protozoa or fungi. Microbial biopesticides are relatively specific for the target pest. For example, there are some species of fungi that are used to control weeds, while others are applied for insect control. The most commonly used microbial biopesticide includes strains and subspecies of Bacillus thuringiensis (Bt). The proteins produced by this bacterium kill specific species of larvae and are used to control insect pests such as moths and mosquitoes.
  
  

Plant-Incorporated Protectants

• Plant-incorporated protectants are biopesticides that the plant itself produces as a result of genetic modification. For example, scientists can take the genetic code for the Bacillus thuringiensis pesticidal protein and incorporate that gene into the plant's own genetic code. In this manner, the plant begins to express the gene for the Bt protein and produce its own biopesticidal substance.
  
  

Biochemical Pesticides

• Biochemical pesticides consist of naturally occurring organic substances that control pests using nontoxic mechanisms. While conventional pesticides are typically synthetic chemical materials that invade and kill the pest, biochemical pesticides tend to use nature's own machinery to control pests and protect the harvest. Some biochemical pesticides include sex hormones that interrupt the mating cycle of a particular pest. Others may use an attractive plant scent to lure the pests into a trap.