The Collaborative International Dictionary
Ferrugo
Ferrugo \Fer*ru"go\ (f[e^]r*r[udd]"g[-o]), n. [L., iron rust, fr. ferrum iron.] A disease of plants caused by fungi, commonly called the rust, from its resemblance to iron rust in color.
Wiktionary
ferrugo
n. A disease of plants caused by fungus; rust.