Haulm: Early attack may cause non-emergence or stunted, pale-green to yellow foliage, upper leaves rolled, stems black and often greasy in region of ground level, stems easily pulled out. Late attack may cause collapse of fully developed haulm. Distinguished from leaf roll and stem canker (Rhizoctonia) by presence of blackened stems at ground level or blackened soft pith in dissected stems.
Tubers: Black rot extending from heel end or from lenticels. The rot may become dry and sunken under dry storage conditions
Mainly seed-borne. More readily spread under wet conditions in field and store
Varietal: Several varieties including Casanova, Estima, Morene, Penta, Record, Shannon, Sierra, Stirling, Symfonia and Vivaldi are very susceptible. Brodick, Kestrel and Saxon show good resistance.
Cultural: Avoid cutting seed. Avoid diseased seed. Ensure adequate field drainage. Store tubers dry and well ventilated. Blackleg-free seed derived from mini tubers may readily become infected. Earlier burning off. Avoid mechanical damage. The use of hot water treatment on seed tubers may reduce inoculum level but stocks of susceptible varieties will readily become re-infected if subjected to conditions favourable for bacterial development. Seed testing for bacterial loading can give an assessment of risk but bacterial levels, and subsequent symptoms can increase rapidly under favourable conditions, or decrease in unfavourable conditions.
Other Erminia bacteria (Erwinia carotovora ssp carotovora and E. chrysanthemi) can also cause symptoms similar to blackleg and contribute to tuber rotting. E. chrysanthemi can cause a slow wilt in the field with darkened vascular tissue and a brown discoloration in the stems.