Spots may be found on the stems, especially during warm, humid weather when growth is lush. The colour of these spots is due to masses of fungal spores which, if touched, leave a reddish-brown smear on the skin. Rust is the only leaf-spotting disease of lucerne with this characteristic. This disease can affect all above-ground parts of the plant and fungus may extend to the crown and upper root. The irregular shaped lesions on the eaves enlarge, join, and become lighter brown.
Affected leaves turn yellow and often wither before falling.
Lesions on the stems enlarge and may encircle and blacken large areas near the base of the plant. The fungus also causes a crown and root rot. Stemphylium leaf spot may cause significant defoliation during warm wet periods. The spots on the leaves are oval, slightly sunken, dark brown with lighter centres and they are usually surrounded by a pale yellow halo. The fungus can also blacken stems.