Iris sp. (Iris) get a leaf diseases caused by Mycosphaerella macrospora which causes lesions that appear to have greasy margins and bacterial rot that decays the rhizome.
The more serious problem is the iris borer that allows the bacterial rot inside the leaf and rhizome that the borer carries in on its body.
The fungal disease likes wet conditions.
The borer enters the leaf when the leaves are about 4-6 inches high. The insect works its way down the leaf into the rhizome. The bacterium follows.