Spring black stem

Phoma medicaginis is one of the most serious necrotrophic pathogens on Medicago sativa (alfalfa). On this crop, the disease is known as spring black stem and leaf spot. Disease symptoms typically include seedling blight, stem canker, and leaf spot. Infected leaves undergo chlorosis and defoliate, while stem and petiole lesions may progress, causing crown and root rot. The disease spreads rapidly in cool and wet conditions because pycnidia within lesions disperse conidia by rain splash.