Sudden Death Syndrome of Soybeans

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Root Symptoms

  • A blue coloration may be found on the outer surface of taproots due to the large number of spores produced
    • These fungal colonies may not appear if the soil is too dry or too wet
  • Splitting the root reveals cortical cells have turned a milky gray-brown color while the inner core, or pith, remains white
  • General discoloration of the outer cortex can extend several nodes into the stem, but its pith also remains white
Root symptoms of SDS -- blue mold
General discoloration of the outer cortex can extend several nodes into the stem.

Leaf and Plant Symptoms

  • Leaf symptoms first appear as yellow spots (usually on the upper leaves) in a mosaic pattern
  • Yellow spots coalesce to form chlorotic blotches between the leaf veins
  • As chlorotic areas die, leaves show yellow and brown areas contrasted against green veins
  • Affected leaves twist and curl and fall from plants prematurely
  • Flowers and pods abort, and seeds are smaller
  • Later-developing pods may not fill, and seeds may not mature
Soybean plants showing SDS symptoms.

Sudden Death Syndrome symptoms

Stem of plant with sudden death syndrome.

Disease Facts

  • Fungal disease caused by Fusarium virguliforme
  • Has spread to most soybean-growing states and Ontario, Canada
  • Continues to spread to new fields and larger areas of infected fields
  • Ranked second only to soybean cyst nematode (SCN) in damage to soybean crop
  • Fungus colonizes only crown and roots of the plant
  • Above-ground symptoms are caused by a toxin produced by the fungus and translocated throughout the plant
  • Severity varies from area to area and field to field

Sudden death syndrome (SDS) of soybeans.


Conditions Favoring Disease Development

  • Cool, moist conditions early in the growing season often result in higher disease incidence
  • Favorable disease conditions may result from early planting, high rainfall and/or low-lying, poorly drained or compacted field areas
  • If SCN is also a problem in the field, disease may be more severe
  • Infection occurs early in the season, but symptoms usually do not appear until midsummer
  • Appearance of symptoms often associated with weather patterns of cooler temperatures and high rainfall during flowering or pod fill

Fusarium virguliforme Disease Cycle

  • Fungus survives in crop debris and as mycelia in the soil
    • Survives best in wet areas such as poorly drained or compacted field areas
  • Fungus enters roots early in the growing season
    • Infection may be facilitated by wounds from SCN, insects or mechanical injury
  • Fungus colonizes the root system
  • Fungus overwinters in diseased soybean residue

Impact on Crop

Soybean seed yield is reduced as:

  • Plants lose leaf area and leaves drop prematurely
  • Roots deteriorate, reducing water/nutrient uptake
  • Flowers and pods abort, resulting in fewer pods and seeds
  • Seeds may be smaller and late-forming pods may not fill or mature

Management of Sudden Death Syndrome

Use a combination of practices:

  • Select SDS-resistant varieties
    • Pioneer has developed elite soybean varieties with improved SDS resistance
      • Soybean breeders have selected for genetic resistance in multiple environments with high levels of natural SDS infection
    • Pioneer rates its varieties and makes ratings available to customers
      • Ratings range from 4 to 8 (9 = resistant), indicating very good resistance is available in elite soybean varieties
  • Your Pioneer representative can help you select suitable varieties
  • Manage soybean cyst nematode (SCN)
    • Plant varieties resistant to both SDS and SCN
  • Improve field drainage and reduce compaction
  • Evaluate tillage systems
    • Where possible, some tillage may be needed to bury infected residue
  • Reduce other stresses on the crop
  • Plant the most problematic fields last in your planting sequence
  • Foliar fungicide cannot protect plants from SDS
Very early symptoms of SDS development on soybean leaf.
Very early symptoms of SDS development on soybean leaf.

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