Q What is sweetcorn smut?

A This spectacular disease likes warm, dry areas and hot summers, when it infects ears of sweetcorn. It is rare for losses of sweetcorn to be serious, despite the alarming appearance of the ears.

Caption: Sweetcorn smut looks alarming but it rarely causes serious losses

Q How does sweetcorn smut develop?
A It spends the winter as tough teliospores that can lurk in the soil for several years. The following year, these teliospores germinate and release clouds of basidiospores, which disperse on the breeze or by rain splash on to young sweetcorn plants. The growths from the fungal spores must mate with compatible types in the host plants if infection is to spread into the plant. Where the fungus threads or hyphae grow, the nearby sweetcorn cells begin to divide and galls are sometimes, but not always, produced. These turn up on the stems, leaves, flowers and ears. Where they infect the ear, as often happens, the whole ear is a mass of swollen distorted gall. The fungus invades the gall and its cells are converted to the tough, dark-coloured teliospores. These are released when the mature gall breaks open, contaminating the soil or, occasionally, germinating and causing new infections elsewhere on the same plant or other plants. Once in the soil, they remain infectious for five years or more.

Q What should I do if sweetcorn smut happens?

A Remove the affected ears and throw them away.