I just read what seems to be a recent re-assesment of the cause of scorch in the book "The Japanese Iris" by McEwan. I tried to copy and paste the quote but evidently Google books doesn't allow this. It is probably a mycoplasma that is vectored by a leaf hopper and the transmission is directly from plant to leafhopper to plant, so evidently you don't need to worry about it contaminating the soil...That is a big relief.
