Systemic infection causes early shoot death and prevents seed production.
A hormone imbalance causes growth of spring shoots from infected roots to be earlier and faster than normal. These shoots have pale green erect leaves about a third the normal width with long internodes and a high transpiration rate. Stem growth ceases after 7 weeks, when spore production starts, while uninfected plants continue to grow. Most infected roots in the spring produce shoots with uninucleate mycelium that forms many reddish-brown pustules on lower leaf surfaces. The summer spores form secondary localized infections on upper leaf surfaces every 6 to 10 days, but the mycelium from these grows so slowly that it only becomes systemic on young plants.