Initially upon hatching from eggs the small borer will chew small pin holes in the leaves. As they mature they work their way downward into the leaf sheath. Eventually the borers will move into the rhizome and hollow it out, reducing it to just a shell. Injury by the borers provides infection sites for bacterial soft rot. Cultural control can be achieved with this insect by a thorough cleanup of the plants in the fall and spring of each year.
Control is based on destroying the eggs.
During division, every few years, all damaged rhizomes should be discarded. A troublesome leaf spot disease on iris is caused by a fungus, Didymellina macrospora . Usually this disease is more common toward the end of the season, on the upper portion of the leaves. It is not as severe with normally dry weather. If the plants are crowded, shaded and the weather is rainy this fungus can cause spots earlier in the season.