I have dug up and disposed of a large clump of older Irises and of course when I did I found signs of Iris Bores.

here's my question, what do I need to do to the SOIL where the irises were planted that would make it safe to replant more Irises? I read here on this forum to pour dishwater on the spot but I don't understand what is in dishwater (beside soap)that may be effective or why not just mix up big buckets of soapy water and use that for treatment?

This fall I intend to use the blowtorch treatment and next spring I will use Merit earlier. I used it this spring but I must have waited too long for it to be effective

Thanks for any information