Survives in alfalfa residue. Spores are spread by air currents. Also can attack clovers. Some varieties may suffer less yield loss, but the reaction of most varieties to the disease is unknown. Rotate away from forage legumes for at least two years.
Seedlings turn yellow to reddish-yellow, wilt, and die.
Established plants regrow slowly following cutting but usually do not show any color change. Infected taproots initially are reddish-brown but become black with age. Infected plants are susceptible to winter-kill. The fungus can survive for 3-5 years in infested soil. Spreads in moving water and in soil on equipment or boots.