Combination and rotation of bacterial antagonists to control powdery mildew on pumpkin

Mixtures of micro-organisms may lead to more effective control of plant pathogens than biocontrol with single species, but little data exists on the efficacy of microbial combinations against powdery mildews. In a field experiment in northern California with high disease pressure, we found, at best, only modest disease control with individual use of three species of commercially-available bacterial antagonists. Application of all species as a mixture or in rotation did not improve disease control more than the best monoculture, suggesting a lack of synergism among mixture components.