Smut diseases aren't common in gardens, but one that is often seen is sweetcorn smut.
A fungus that is spread by water (rain or other) splashing from the infected plant to one nearby or from the soil onto a plant. The fungus mostly attacks the stems of plants although in flowering plants it can infect the tips of the stamen in the flower. Dark coloured spots swell and can explode scattering large amounts of sooty black spores.
Smuts can be identified by small dark spots on stems. Larger dark swellings again on stems often accompanied by leaf distortion. Sometimes swelling and distortion of a flower’s stamen.
Remove and destroy any affected part of the infected plant. Avoid splashing water around the affected plants. There are no fungicides approved to control smut diseases.