Pesticides may affect symbiosis in several ways: by reducing survival or growth of rhizobia; by inhibiting the nodulation process directly, or indirectly by causing abnormalities in plant growth and metabolism; or by influencing nitrogen fixation. Herbicides are compounds which possess phytotoxic activity. High concentrations of some herbicides induce physiological changes in rhizobia. To effectively supply micronutnents and growth factors necessary for microbial growth in vitro, multiple nutrient sources such as the homogenates of various animal organs or yeast extracts are commonly used. The effect of dinitroaniline herbicides on the growth and symbiosis of legumes has been investigated. The effect of triazine herbicides on the growth and symbiosis of legumes has been the subject of several studies. Protectant fungicides are commonly used to aid in the establishment of legume crops and pastures by protecting the seedlings from soil-borne fungal pathogens. In general, rhizobia are more susceptible to fungicides in vitro than when growing in situ.