Rust

Rust is a parasitic fungi that form dry reddish, yellowish, or orange spore masses on infected tissue.  The upper surface of heavily infested leaves turns yellow or brown and may drop prematurely.  This can cause branch dieback and occasionally kill the plant.  Rust is spread primarily by windblown or water splashed spores.  Fungicides applied in the spring can reduce some rust disease.  Fungicide injections may also be done.