Black root rot is an intractable soil borne disease that threatens the sustainability of Australian cotton fanning. In this paper we describe the factors contributing to the spread of black root rot, the effects of black root rot on the maturity and yield of cotton, and prospects for its management and control. Black root rot was first observed in Australian cotton in 1989 (Allen, 1990). Annual disease surveys have shown an exponential increase in the number of fields with black root rot in NSW (Figure I) and the disease now occurs in all cotton glowing regions of NSW except Menindee. Black root rot is also widespread in south west Queensland and the Darling Downs (J. Kochman, personal communication). All understanding of the life cycle of the pathogen, Thielaviopsis basicola (Figure 2), is a key factor in explaining the increasing spread and severity of black root rot. T basicola is a soil borne fungus that produces two types of spores; thick walled chlamydospores and thin-walled endospores (Figure 2). Both spore types can cause disease. The spores of T basicola are primarily soil borne but may also occur internally with stem rot (Figure 2). Consequently, most spread of T basicola is by movement of soil, carried either in moving water or on vehicles and machinery.