The fungus, Neozygites fresenii, is a valuable natural enemy of the cotton aphid, Aphis gossypii. This fungus has caused epizootics each year since 1988 throughout cotton growing areas in the mid-South and Southeast. In many cases the fungus reduces high aphid populations to below economic thresholds. The fungus has a complex life cycle precisely coordinated with periods of high relative humidity. Aerial spores in cotton fields are important in the rapid transmission of the fungus throughout a field. Regular scouting of cotton fields and accurate diagnosis of the fungus can lead to less reliance on chemicals for aphid control.