Compositions and methods are provided for enhancing plant immunity, health, growth and yields, as well as enhancing rhizosphere properties, using beneficial microbes and/or their growth by-products. Specifically, the subject invention enhances plant health, growth and/or yields by applying a yeast-based composition to the plant (e.g., the roots) and/or its surrounding environment (e.g., the soil). Specifically, in one embodiment, the subject invention utilizes the killer yeast Wickerhamomyces anomalus and/or a species related closely thereto.