Bean rust

Uromyces appendiculatus

Rust symptoms initially appear as small yellow or white slightly raised spots on upper and/or lower surfaces of leaves. These spots enlarge and form reddish-brown or rust-colored pustules that are about 1/8 inch in diameter and contain thousands of microscopic summer spores (urediniospores). Spores (fungus seeds) are readily released from the pustule and give a rusty appearance to anything they contact. Rust can be distinguished from other leaf spots in that these spores rub off onto your fingers, while blights and bronzing do not.
Pustules may be surrounded by a yellow border. Severe infection may cause leaves to curl upwards, dry up, turn brown and drop prematurely. A severely damaged bean field often looks like it has been scorched. Pod set, pod fill and seed size can be reduced if early infection is severe. Green pods, and occasionally stems and branches, also may become infected and develop typical rust pustules. However, bean rust is not seed-borne.

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