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Diaporthe Stem Canker

Causal Agent:

Diaporthe aspalathi and Diaporthe caulivora; part of the Diaporthe species complex, which includes pathogens of Phomopsis seed decay, pod and stem blight

Symptoms and Signs:

  • Premature plant death near end of growing season with leaves still attached
  • Sunken, reddish-brown lesions on stem
  • Cankers may begin in late vegetative stages and expand rapidly
  • Black zones lines in lower stem to upper tap root
  • Interveinal foliar chlorosis or necrosis

Disease Cycle:

  1. Fungal bodies can survive in plant residue for years in the soil. Infected seed is also a source of inoculum.
  2. Spores are splashed by rainfall to soybean stems. Wet weather will favor pathogen infection and development.
  3. With persistent rainy weather, cankers rapidly develop in late vegetative to early reproductive stages of the soybean.
  4. Secondary infection can occur throughout the season, though it does not have a great impact on disease development.
  5. Plants may die prematurely with leaves still attached.

Disease Management:

Host Resistance: Moderate to highly resistant varieties are available to manage stem canker. Host resistance is the primary and most effective method of managing stem canker.

Healthy Seed: Do not use seed from an infected crop. This disease is seedborne and endophytic, so even if seed looks healthy, germination rates will likely be very poor.

Crop Rotation: Rotate the field to a non-host crop, such as corn, wheat, or sorghum, for growing seasons immediately following an outbreak. This will reduce the amount of viable inoculum in your field by eliminating its host for a full growing season.  Do not rotate in alfalfa.

Tillage: Deep plowing or any form of tillage that will aid in breaking down the Diaporthe colonized residue can be effective in reducing infection.