Is it affecting the performance of the irises? How badly does disfigure the foliage? Is it something you could simply live with?

"I have little brown spots on a few of my iris clumps"

May we see a photo?

I am not a fan of treating conditions/diseases that have not yet been accurately identified. IMO the first step is always going to be to identify the problem to a certainty. Then and only then will I start researching controls.

I see that in wet years. My soil is heavy clay so iris here should be located in full sun in raised beds or on slopes. If I transplant the spotty iris to a drier locale, they are fine the following year.

https://pin.it/BznZY8B see if this link works, exactly what I'm dealing with