Seasonal development and life cycle—Rust
Rust is favored by temperatures between 55° and 90° F. Several hours of dew or rain are necessary for spores
to germinate and infect the host. Rust is most common on fern growth after the harvest season is over.
Infections begin in spring from spores that overwintered on crop debris. These infections produce the
orange stage of the disease. Light green patches that mature into yellow or pale orange pustules in concentric
ring patterns develop on new spears. Spores produced by these spring stages are airborne to new fern growth.
Infection occurs and brick red pustules develop on stalks, branches, and leaves of the fern. These red
pustules produce airborne, rust-colored spores in a powdery mass, which can reinfect the fern and increase
disease incidence. As ferns mature and die, the black-spore stage may develop. These black spores are
the overwintering stage of the fungus.