Technical improvements in the production and formulation of microbial agents will increase the potential for development of biological pesticides that are able to compete with chemical insecticides in the marketplace. Here we report the efficacy of a simple granule formulation containing microsclerotia of Metarhizium brunneum (Petch) (Hypocreales: Clavicipitaceae) for control of unfed and fed nymphs of Ixodes scpaularis Say (Acari: Ixoididae). Microsclerotial granules of M. brunneum applied to moist potting mix produce infective conidia within 2 wk and conidia remained viable for up to 8 wk after application. Microsclerotial granules produced from 3.05 x 10(9) to 1.24 x 10(10) conidia g(-1) granules in potting mix. Both unfed and fed nymphs were susceptible to infection when exposed to treated potting soil with up to 56 and 74% mortality, respectively. M. brunneum demonstrated a transtadial infection for fed nymphs exposed to treated potting mix with signs of a fungal infection becoming apparent only after molting into adults. High conidial production rates from microsclerotial granules of M. brunneum combined with significant tick mortality support the need for additional research to evaluate the efficacy of this treatment technology as a biopesticide option for control of ticks.