Stem Canker


  • Initial symptoms are reddish brown, slightly sunken lesions that appear at the base of branches or leaf petioles.
  • These lesions can develop into elongated, sunken, dark brown cankers.
  • Brown discoloration may also occur inside the stem.
  • Plant parts above the lesions may die.
  • Leaves may develop necrosis and chlorosis between the veins, and may remain attached after death.
  • Lesions may be found at the soil line, making it easy to confuse this disease with Phytophthora rot.
  • Stem canker does not cause root rot, while Phythophthora rot causes root rot.
  • Tiny black dots may appear on the stem singly or in clustered groups on plants killed by stem canker.

Pathogen Involved:

  • Diaporthe phaseolorum var. caulivora, a fungus that causes northern stem canker.
  • Diaporthe phaseolorum var. merdionalis, a fungus that causes southern stem canker.
  • These pathogens overwinter in infested soybean residue, and may be spread with infected seed.

Time of Occurrence:

  • Mid-July to maturity.

Conditions Favoring Disease:

  • Prolonged wet weather, especially early in the season.
  • Conservation tillage.
  • Yield losses can be significant.

Disease Management:

  • plant resistant or moderately resistant varieties
  • delayed planting may be beneficial
  • foliar fungicides may be beneficial
  • tillage can reduce disease problems in fields where stem canker has been a problem