Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales

There are an estimated 168 rust genera and approximately 7000 species, more than half of which belong to the genus Puccinia. Rust fungi are highly specialized parasites with several unique features.

Unlike other plant pathogens, rust usually affects healthy and vigorously growing plants, so the infection is limited to plant parts such as leaves, petioles, tender shoots, stem, fruits, etc. Infection may cause deformities such as growth retardation, witch's broom, stem canker, or formation of galls.

Plants with severe rust infection may appear stunted, chlorotic (yellowed), or otherwise discoloured

Rust is most commonly seen as coloured powder, composed of tiny aeciospores which land on vegetation producing pustules, or uredia, that form on the lower surfaces.