Pathogen(s) causing disease:

Ustilago tritici

Symptoms:

Infected heads are blackened with a dry, powdery mass of fungal spores. Entire seed is replaced by black fungal spores. These spores are soon blown away, leaving the rachis of the head bare. Heads of infected plants usually emerge from the boot slightly earlier than normal. Prior to heading infected plants may have dark green, erect leaves, sometimes with chlorotic streaks.

Conditions:

Disease is favored by cool to moderate temperatures and humid conditions. Infections only occur during flowering.

Management:

Pathogen-free seed, systemic fungicide seed treatment, resistant varieties. Loose smut reduces yield in proportion to the percentage of smutted heads in the field. To estimate the loss per acre, several hundred heads must be examined randomly in the field to determine the percent which are smutted. The net loss can be calculated by multiplying the following: percentage of smutted heads by a factor of 0.8 (if less than 5 per cent smut) or 1.0 (if greater than 5 per cent smut) by the yield per acre in bushels by the current selling price of wheat.

Sources:

Purdue UniversityPurdue University
The Ohio State UniversityThe Ohio State University