The mechanism of spread of this disease is similar to that of spring black stem. The bacterial diseases typically do not cause detectable yield loss, but can do so occasionally. Bacterial leaf spot is caused by Xanthomonas campestris pv. alfalfa . Symptoms are initially diffuse, yellowed areas on leaves, within which tiny water-soaked spots develop. Later, the areas die and dry out, leaving irregular, papery, tan lesions.
Defoliation can follow.
Bacterial stem blight is caused by Pseudomonas syringae pv. syringae , and its symptoms include water-soaked lesions on the stems. Severely affected stems die, with the leaves turning water-soaked and pale yellow. Eventually entire leaves die and dry out. This problem often is associated with early-spring freeze injury, although that would not be the case this year. This information subject to a usage policy .