Efficacy of Bacillus sphaericus formulations against Psorophora columbiae larvae in small rice plots.

Bacillus sphaericus formulations were evaluated against Psorophora columbiae larvae in small rice plots. All formulations tested provided good control (greater than 84%) for all rates tested at 2 days posttreatment. At 10 days posttreatment, fair control (greater than 70%) was recorded for ABG-6232 (0.184 kg/ha), ABG-6262; 27-242-BA (0.766 and 2.298 liters/ha), and ABG-6262; 29-293-BA (2.298 liters/ha). At 7 days posttreatment mortality was below 66%. Control did not exceed 27% at 15 days posttreatment for any formulation tested. Application rates for all formulations tested had little relationship with observed mortality, and control levels often were greater at the lower dosages tested. Bacillus sphaericus provided an effective means for controlling Ps. columbiae, but additional research is needed to determine the lower limit of effective treatment dosages and spore persistence in the rice field environment.