Casing soil is the main doorway for wet bubble disease. DMR records that its spores survive up to three years in casing soil, so last season's soil is a risk, not a saving.
The heat route is one every grower can check: steam treatment of casing soil at 54.4 C for 15 minutes. TNAU steams casing soil in a pressure cooker for 45 minutes. The manual also allows autoclaving at 15 psi for one hour.

