Question
what causes loose smut of wheat and corn

Answer
Like common bunt, loose smut, caused by Ustilago tritici, also is a seed-borne disease of wheat. U. tritici is unique among the wheat smuts in that it it is incorporated into the developing kernel and persists inside the seed. Affected seeds show no symptoms and outwardly appear healthy. Generally, yield losses attributed to loose smut in the Great Plains are low, i.e. less than 1 percent annually. Unlike common bunt, the presence of U. tritici in seed has little effect on grain quality for milling or feed, but the infected seed should not be used for planting without first being treated with a systemic fungicide.