Hi Janos - yes, this group of seedlings is the least resistant to leaf
spot of any that I have grown. However, the late freeze did more damage
to foliage than the fungus.
Heavy dew is on foliage until afternoon here. My breeding includes
selecting seedlings resistant to leaf spot, so I don't spray.
The iris rows are in a sheltered valley with poor air circulation - much
dew and frost.
> I think you have some Heterosporium iridis infection on the leaves
Linda Mann east TN USA zone 7b