Cause A fungus, Uromyces trifolii var. fallens, that is favored by cool, wet weather. Disease usually appears later in the growing season, so it does not usually cause economic losses. Rust was found in an Oregon red clover seed field during 2011, a growing season with cooler- and wetter-than-normal weather.
Symptoms Reddish, brown pustules develop on stems, petioles, and usually the underside of leaf surfaces.
- There are varieties that are less susceptible to rust.
Chemical control Is not usually necessary.
Reference Diachun, S., and Henson, L. 1974. Dominant resistance to rust in red clover. Phytopathology 64:758-759.