Phoma macdonaldii is the causal agent of black stem disease of sunflower (Helianthus annuus L). In France, the incidence and severity of the disease increased dramatically in the early 90s and the entire sunflower cropping area is now affected. Premature ripening appeared in 1994: it is at the present time one of the most widespread and detrimental diseases of sunflower. Recent investigations confirmed that stem base girdling canker due to P. macdonaldii is the primary cause of this syndrome. Crop management and varietal susceptibility can influence significantly the incidence and severity of P. macdonaldii attacks and premature ripening. Partial resistance and presence of tissue-specific resistance genes have also been demonstrated.