H. solani is a fungal pathogen of potato tubers, but can likely survive in the soil as a saprophyte. Infection occurs during the growing season from either seed-based inoculum, or from soil inoculum. Damage by silver scurf worsens during storage by spreading on and between tubers.
Silver scurf is distributed mostly on seed tubers, and is in fact commonly found on them. It is suspected to also move via contaminated soil.
Potato disease specialists in the Northwest recently published a bulletin on silver scurf that we highly recommend. It can be found in the research library section of this website and searching for “Silver Scurf Management in Potatoes.”