The pathogen P. medicaginis is an ascomycete and can cause leaf spot in crops like red clover.

[3] The first symptoms of leaf spot are small circular lesions that form on the lowest leaves on the plant.

[10] Common leaf spot can be found anywhere that alfalfa is grown, but prefers cool, moist conditions, and acidic soils.

During a rainy season, the dense canopy of alfalfa traps the humidity and makes the perfect environment for the pathogen, giving rise to common leaf spot.

Harvesting early will prevent further defoliation of the current crop, which will preserve some of the quality and yield.

Harvesting early also allows the field to dry out, and reduces humidity in the phyllosphere making conditions less ideal for the pathogen.

[11] Applications of potassium fertilizer can minimize yield loss, severity, and leaf drop.