The swelling occurs because of infection with the smut fungus "Ustilago esculenta". The success of the crop depends on the smut fungus. Microbotryum violaceum, also known as the anther smut fungus, was formerly known as "Ustilago violacea". The success of the crop depends on the smut fungus "Ustilago esculenta". The smut fungus "Ustilago maydis" uses an alternative route. The flag smut fungus, "U. agropyri", is a basidiomycete. The Mist flower smut fungus has been employed with some success against the species.