Fungicides such as Daconil 2787, mancozeb, Cleary's 3336, and Chipco 26019 can be used to protect iris from Didymellina leaf spot. Fungicides will not control bacterial leaf spot. Rhizome and bulb disorders Bacterial soft rot is a serious rhizome disease that can appear in newly planted as well as mature iris plantings. Erwinia carotovora causes a foul-smelling soft decay of the rhizome. The bacterium gains entrance into the plant through wounds in young leaves made by young larvae of the iris borer.
Soft rot is prevented by planting healthy rhizomes and eliminating the iris borers.
Botrytis convoluta and Sclerotium rolfsii are two fungi that can cause rhizome and crown rot diseases of iris. The former produces irregular black sclerotia in the decaying rhizome, while the latter produces small spherical sclerotia on the rotted leaf bases. Neither produces a foul-smelling decay. Remove and destroy affected rhizomes. Several other diseases such as black rot, ink spot, Fusarium basal rot, and blue mold cause decays of bulbous iris.