The presence of Phaeomoniella chlamydospora and Phaeoacremonium spp., the causal organisms of Petri disease of grapevine, in canes of rootstock vines in four mother blocks was determined monthly by means of isolations from the basal and fourth internodes. The canes were generally free from fungal, yeast and bacterial infection with only 2.4% of the total number of isolated xylem segments colonised. Basal internodes exhibited three-fold higher levels of infestation. The incidence of Pa. chlamydospora and Phaeoacremonium spp. was extremely low (< 0.2%) in the symptomless canes sampled from these rootstock mother vines. This emphasises the need for more sensitive detection techniques to be used for phytosanitary evaluation and research.