Stem canker is caused by a fungus, Diaporthe phaseolorum var. meridionalis. Initial symptoms appear as small reddish brown spots on stems near a lower node. These spots develop into cankers that can be several inches long running up the stem from the point of infection but only on one side. As the plant dies and the stem turns brown, the cankers are difficult to distinguish from the rest of the stem tissue. Foliar symptoms appear during reproductive growth stages and first appear as yellowing between the veins being more apparent on one side of the affected leaves. These leaves later turn brown and die but remain stuck to the stem, similar to plants affected by charcoal rot. Affected dry plants can easily break over when pushed. The pith of the stems will turn a light brown instead of remaining white and healthy. In some cases the pith may not be used for diagnosis if Dectes stem borer is present which will have caused a dark- brown pith.

  • Variety selection – resistant varieties should be planted in problematic fields, fungicides have been inconsistent and not been effective once foliar symptoms develop. See yearly variety disease ratings pdf publications here and searchable database (link created once ready).
  • Rotation to non-host for 2 years can reduce the pathogen population
  • While this disease has foliar symptoms, no foliar fungicides will manage this disease

Canker on one side of stem

Stem canker susceptible variety on left, resistant variety on right

Stem canker lesions

Yellowing between veins more apparent on one side of affected leaves

Light brown pith of infected plant with stem canker

Beginning symptoms of SDS – small yellow spots

Progression of SDS with interveinal yellowing and dead, necrotic tissue

Center pith remaining white, while water-conducting tissue (xylem) has a gray to brown color in SDS affected plants