Verticillium wilt has been recognized as an important disease of cotton in Australia for many years. The common use of very susceptible cultivars resulted in an increasing incidence of the disease until 1990 when a high yielding resistant cultivar was released. The incidence of the disease has subsequently declined considerably. Black root rot, Fusarium wilt, Alternaria leaf spot and bacterial stunt are relatively new diseases which have rapidly increased in importance. The widespread adoption of reduced tillage practices with the retention of crop residues from season to season, the use of susceptible cultivars and the movement of pathogen inoculum in crop residues and soil by flood and irrigation water and on agricultural machinery have contributed to an increasing disease problem.