Summer Black Stem and Leaf Spot


  • New leaf spots on leaves and stems are usually chocolate to reddish brown and often are fairly large (2-6 mm in diameter) with a fuzzy margin.
  • Spots turn a silvery tint and often have a chlorotic halo around them.
  • A few lesions can cause leaflets to fall off the plants.
  • More than one leaf disease often occurs at the same time on a plant.
  • Leaf diseases vary according to the rates of stem and leaf growth, and are influenced by humidity, temperature, and light intensity

Pathogen Involved:

  • Cercospora medicaginis (a fungus)
  • Overwinters in infected stems

Time of Occurrence:

  • Summer leaf spot and black stem usually begins on or after the second cutting.

Conditions Favoring Disease:

  • Warm to hot, wet and humid weather

Disease Management:

  • Cultivars with high levels of resistance are not available, but some cultivars appear more resistant than others
  • Harvesting early is recommended to reduce loss of quality and yield.