I'm guessing scorch too, but I've never had iris borers. I'm thinking borers cause more rotting in the leaves, although more in the rhizomes. I have had plants that looked like this, I thought was scorch, but mine was due to intense summer heat. I've never lost any plants from it, I just cut back hard & pulled off the dead foliage. I just looked up scorch, & didn't realize there is an actual disease though. the article I read says heat may be a solution. Dig out the plant, cut off any unhealthy parts, and expose to sunlight for a few days before replanting-preferably in a different place.

When I grew ABs they did this in the heat of the summer, some of them recovered others just died on out. I lost my last one when I tried to dig it when I amended the bed it was in.. I just gave up on trying to grow them here.