Rust
/RUST/🦠 Diseases● Basic
Also known as: rust disease, uredinia
A group of fungal diseases (order Pucciniales) characterised by the formation of powdery, often orange or rust-coloured spore-producing pustules (uredinia) on leaves, stems, and sometimes fruits. Rust fungi are obligate parasites — they can only grow on living host tissue. Many are heteroecious, requiring two different host species to complete their life cycle (e.g., cedar-apple rust alternates between junipers and apples).
Etymology
Old English rūst (rust), from Proto-Germanic rustą (redness)
Example
“The orange pustules on the underside of these hollyhock leaves are caused by hollyhock rust (Puccinia malvacearum).”