- Silver scurf (Helminthosporium solani) is a free-sporulating, seed borne, fungal disease which can spread rapidly.
- The disease can spread to tuber surfaces which are not infected or protected by a seed treatment.
- Competition occurs between silver scurf and black dot, with the result that control of one disease may result in greater infection by the other.
- More …
- Transmission of infection and disease development.
- Conidiophores form at the edges of lesions on tubers.
- After planting, conidia (spores) may be released into soil and transferred to developing tubers by movement of water, though it is also suggested that the fungus can grow along roots or stolons and thus reach progeny tubers.
- Progeny tubers may be infected at any stage of development but may be more susceptible after the periderm (skin) has begun to mature.
- Infection can occur through lenticels and directly through the periderm but hyphae are confined to the periderm.
- The number and size of lesions increases with duration of tuber growth.
- Silver scurf can remain viable in soil for two years but as potato is the only known host soil borne inoculum should not occur in a potato rotation unless there is a problem with volunteers.
- More …
Risk of silver scurf
- There may be a greater risk of silver scurf infection from apparently clean than from infected seed (lesions which have sporulated are unlikely to produce further inoculum).
- The disease increases during the season and the risk is thus increased by later dates of harvest.
- The risk of disease development in store increases if condensation occurs on the tuber surface.
Inspecting seed for silver scurf
American University Extension Services suggest the following method for inspecting seed before purchase, to determine whether lesions will sporulate.
- Place a sample of 25 – 50 washed tubers in a plastic bag containing moist paper.
- Seal the bag, punch a few holes (about 1.5 mm).
- Store in the dark at 15 – 24 oC for 2 – 3 weeks.
- Do not allow tubers to dry out.
- Use a hand lens to inspect for conidiophores at the edges of lesions.
- Silver scurf on the seed may be controlled by imazalil (e.g. “Gavel”) and by thiabendazole (e.g. “Storite Excel”) applied during storage but resistance to thiabendazole has been developing. More …
- There is also some evidence of disease suppression by flutolanil (“RhiNo”) and by fludioxonil (“Maxim 100FS”) (more …).
- Poor control usually results from uneven application of seed treatments.
- In the past some problems with poor crop emergence or performance have been associated with two applications of imazalil (i.e. to seed going into store and before planting) and there are now manufacturers’ restrictions to use – check manufacturers’ recommendations before use. See also: Seed treatment.
- Prevention of condensation in stores reduces the risk of disease development during storage. More …
See the manufacturers’ websites for details of agrochemical use.
Silver scurf notes
Transmission of seed borne diseases 2018 (Life cycle; spread of disease; inspection of seed)
Seed treatments 2009 (Fludioxonil and flutolanil experiment results: some control of silver scurf)
Silver scurf 2001 (Cultivars vary in susceptibility; variation in efficacy of seed treatment application systems)
Tuber blemishing diseases 1999 (Includes silver scurf: a free-sporulating disease which can spread rapidly over the tuber surface; )
Tuber blemishing diseases 1998 (Includes silver scurf: there is a negative relationship between seed tuber and progeny tuber infection; condensation in store allows disease development; seed treatment efficacy depends upon coverage; silver scurf and black dot compete on the tuber surface)