Phytophthora nicotianae is an important root and stem pathogen of tobacco (Nicotianae tabacum L.) in South Africa. Growers strive to control the resulting disease, known as black shank, with metalaxyl treatments and by planting resistant cultivars. P. nicotianae isolates associated with black shank in South Africa were selected in order to evaluate their aggressiveness, designate races and to evaluate tobacco cultivars resistance to them. Stem inoculations were conducted in the greenhouse using 32 P. nicotianae isolates from different tobacco growing regions in South Africa. These isolates differed significantly in levels of aggressiveness. Eight isolates were selected on the basis of geographical origin and virulence for race characterization using a set of differential tobacco cultivars. Race 0 and 1 of P. nicotianae occurred in most of the tobacco growing regions. Commercially planted cultivars differed significantly in their resistance to race 0 and 1. A further aim was to consider whether metalaxyl resistance has contributed to poor disease control and if recently developed cultivars with high levels of resistance require metalaxyl for effective control. One hundred and thirty two isolates of P. nicotianae were screened for metalaxyl resistance. P. nicotianae isolates from most tobacco farms were metalaxyl sensitive. Growth of most isolates was inhibited completely at 1.0 µg/ml with the exception of isolates from the MKTV tobacco producing area where EC50 values ranged from 1.02 µg/ml to 3.57 µg/ml. Twenty-one tobacco cultivars were planted and treated with and without metalaxyl. Metalaxyl reduces black shank severity significantly in susceptible cultivars in the field but the use of metalaxyl in combination with moderately resistant cultivars effectively controls black shank in the field. Resistant cultivars were healthy and no significant differences between the metalaxyl treated and untreated plants were observed.