ARAgriculture Home Loose Smut Loose smut, caused by the fungus, Ustilago tritici, is strictly a seedborne disease. Symptoms are very obvious at heading because the entire head is replaced by a mass of dark brown, powdery spores. The spores soon blow away leaving a bare stem.
Spores enter florets of healthy heads at flowering time and germinate to infect the developing seed.
The fungus remains dormant in the seed until the seed germinates. Infected seed appear similar to healthy ones. After the seed germinates, the fungus infects the growing point of the seedling and remains associated with the growing point until it invades the developing head and the disease cycle is completed. Several seed treatments are effective in preventing the pathogen in infected seed from becoming established in the growing point of the seedling. Several generations of seed in a row need to be treated to completely eliminate the pathogen from infected seed lots.