I noticed that some of my iris's were browning and suddenly they seemed to just disappear. When I dug into the garden I found many empty husks of rhizomes. Additionally they few that were left were orange on the inside instead of white and smelled of sulfur and decay. There seemed to be a number of parallel holes in the rhizomes but I thought this could be where roots had previously emerged from the rhizome.

I have been growing iris in this spot for 20 years without any difficulty. I cut off the bad sections and washed them off. Interesting fact was that some of the decaying rhizomes were sending up new green shoots.

Is this insect damage or is this a microbiological infection? What is the best way to treat it and the surrounding soil? I have an oxygen based food safe bleach that is used in the beverage industry to sterilize containers, will this work?