Ustilago tritici (Pers.) Rostr.

1. Symptoms: The entire inflorescence, except the rachis, is replaced by masses of smut spores (picture on left). These black teliospores often are blown away by the wind, leaving only the bare rachis and remnants of other floral structures (picture on right).
2. Development: Wind blown teliospores that land on the flowers of wheat plants can germinate and infect the developing embryo of the kernel. The mycelium of the loose smut fungus remains dormant in the embryonic tissues of the kernel until the kernel begins to germinate. The mycelium then develops along with the growing point of the plant, and at flowering time replaces the floral parts of the spike with masses of black spores. Infection and disease development are favored by cool, humid conditions, which prolong the flowering period of the host plant.
3. Hosts/Distribution: The disease can occur wherever wheat is grown.
4. Importance: Yield losses depend on the number of spikes affected by the disease; incidence is usually less than one percent and rarely exceeds thirty percent of the spikes in any given location.