Causal Agent

Phoma medicaginis var. medicaginis

 

Hosts

Alfalfa

 

Symptoms

Spring black stem occurs in the northern United States during early spring and reduces forage yield and quality. Many small, dark brown spots develop on the lower leaves and stems. Leaves, especially lower ones, turn yellow, wither, and fall off. Lesions on stems enlarge and may blacken large areas near the base of the plant. Severe infestations girdle and kill the stem. The plant dies when infection spreads to the crown and roots. Cutting the stand at early stages of maturity will reduce leaf loss and disease prevalence. Currently available varieties have variable levels of resistance, but none are characterized for this disease.

 

Control

Please contact your local county extension office for current information.