In a broad sense, biocontrol can be defined as the manipulation of a root or soil environment, through non-chemical means, to reduce the activity of pathogens. This broad definition includes the use of resistant cultivars, cultural practices and the introduction of beneficial microorganisms into the root zone. The cotton disease biocontrol program at the Australian Cotton Research Institute focuses on the use of beneficial microorganisms to control cotton diseases. Several naturally occurring bacteria are antagonistic to pathogens. These bacteria are referred to as biocontrol agents. When introduced into the root zone, the biocontrol agents can interfere with the activity of the pathogens.