These are always a source of danger, even when the seed is treated with fungicides before sowing.
"There are also chances for the infection of a crop if absolutely smut-free seed is employed.

First, soil infection from a previous smutty crop; second, soil infection from wind-blown spores.

Experiments have shown that separated spores from crushed smut balls lose their effective power in from two to three months, provided the soil is moist and loose, and in no case do they survive a winter.
"It does not seem probable that wheat smut will be controlled by any single practice, but rather by the combined use of various methods: crop rotation; the use of clean seed; seed treatment with fungicides; cultural practices and breeding; and selection of varieties.
"Failure to practise crop rotation is undoubtedly one of the main explanations for the general prevalence of smut in the wheat-fields of eastern Washington.

Even with an intervening summer fallow, the smut from a previous crop may be a source of infection.

Experience shows that a fall stubble crop is less liable to smut infection than a crop following summer fallow.