SDS in Soybeans

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

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

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

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

• 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

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