During the 1990s, silver scurf (causal agent Helminthosporium solani) emerged as an economically important disease of table stock and processing potatoes (Solanum tuberosum). The pathogen attacks the periderm of the potato tuber causing blemishes. The disease cycle of silver scurf has both field and storage phases. Primary infection occurs in the field and high relative humidity favours the spread and increase of silver scurf in potato stores. Control of the disease by chemical and cultural practices remains difficult. Increase in disease has been attributed to H. solani isolates resistant to the postharvest fungicide thiabendazole (TBZ). Polymerase chain reaction (PCR)-based detection methods for H. solani and TBZ-resistant isolates are rapid and more specific than traditional identification. This review discusses the biology of the pathogen, epidemiology of the disease, detection of the pathogen and integrated control measures for the management of silver scurf in both field and potato tuber stores.

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The development of resistance to a post-harvest and preplanting benzimidazole fungicide, thiabendazole (TBZ), has resulted in the increase of silver scurf of potato caused by Helminthosporium solani. Conventional and polymerase chain reaction (PCR)-based assays were compared, among 54 isolates of H. solani, to detect the TBZ-sensitive (TBZS) and -resistant (TBZR) isolates. In a PCR-based assay, all 27 single-spore isolates from eastern Canada, nine isolates from Alberta in western Canada, six isolates from North Dakota, USA were distinguished as TBZR, the remainder of the isolates being determined as TBZS. The results from the PCR-based assay correlated well with the TBZ sensitivity assessment of isolates of H. solani on the TBZ-amended medium. Also, the detection of TBZR- H. solani in 20 tuber samples with silver scurf lesions by the PCR-based assay demonstrates that this method can be used to detect the pathogen directly from the tuber lesions. The PCR-based method was more rapid (1 day) than the conventional technique (5 weeks).