Bipolaris sorghicola (isolate BS1) and an unidentified Bipolaris species (isolate BX1) were isolated from johnsongrass in North Carolina. Inoculum of BX1 was mass produced in solid and liquid cultures, whereas inoculum of BS1 could only be produced in solid cultures. When six formulations of inoculum of BX1 were compared, vegetable oil was the best adjuvant. Isolate BX1 displayed some host specificity in pathogenicity tests. In the greenhouse, isolate BS1 was more virulent on johnsongrass than isolate BX1. In growth chambers, increasing conidium concentration and younger plant ages interacted to increase virulence of BX1, as did interactions between inoculation, johnsongrass density, and low soil fertility. In Raleigh, NC, isolate BX1 caused very little damage in the field, with or without pretreatment with metolachlor. In Greenville, MS, isolate BX1 caused significant (52%) mortality to annual johnsongrass with very little damage to corn or grain sorghum. The biocontrol potential of the two organisms is uncertain.