Various salts of mercury have been found effective in checking injury by such soil inhabiting pests as the cabbage maggot (Iiylemyia brassicae), the carrot rust fly (Psila rosae), and the onion maggot (Ilylemyia antique). Of the various compounds examined mercurous chloride is especially noteworthy, as much on account of its great safety to the crop treated as because of its efficiency as an insecticide. Mercurous chloride promises to be an exceedingly useful insecticide, particularly in the treatment of tender crops such as cauliflower and celery seedbeds, as well as in certain types of greenhouse work. In addition to its insecticidal properties, mercurous chloride also appears to have considerable fungicidal value in checking certain seedbed diseases.