There are many diseases that can impact soybean productivity, reducing yields and quality. Seedling diseases, caused by Pythium, Phytophthora, Rhizoctonia and Fusarium are examples of pathogens that can impact soybeans in Illinois. Other lesser-known diseases including red crown rot and taproot decline may establish themselves in the state. This talk will go over identification, management and other considerations to make with seedling diseases in soybeans.

1 CEU in Integrated Pest Management

Presenter: Nathan Kleczewski, Assistant Professor, University of Illinois

Nathan Kleczewski is a Research Assistant Professor at the University of Illinois. He conducts research and extension activities on plant pathology issues in the state focusing on corn, soybeans and wheat.

Soybean Seedling Pathogens

• Similarities:
  • Soilborne
  • Favor excessive soil water
  • Overwinter in residue
  • All cause a root rot and can either impact stands (killing seedling before it reaches soil line or soon after) or impact growth rate, production (low areas in fields)
• Differences:
  • Physiology, genetics
  • How they interact with host
  • Host range
  • Management options

Pythium

• Symptoms
  • Can be mushy roots
  • Rat-tailing
• Lots of Pythium isolates in Illinois—complex population of Pythium in our fields and can affect management differently
• Differ in aggressiveness by species
• Temperature can impact amount of disease caused by Pythium and the benefit of fungicides
  • P. aphan more efficient and causing disease at warmer temperatures around 69 degrees F – see benefit of fungicide at higher temps
  • P. ultium not really impacted by temperature
• Management:
  • Minimize compaction; address drainage issues
  • Plant into warm soils
  • Seed treatment with Pythium-specific active ingredients (2-3 weeks of initial protection)

Phytophthora

• P. sojae most common followed by P. sansomeana
  • sojae is more aggressive and specific to soybeans
• Unlike Pythium there is resistance to Phytophthora
  • Field tolerance—general/partial resistance
  • Race-specific genes—complete resistance
• Management:
  • Avoid compaction
  • Use variety with good field tolerance
  • Consider Phytophthora fungicide seed treatment

Rhizoctonia

• Symptoms:
  • Late infection typical—stunted yellowed plants
  • Wilting, especially during mild drought
• Management:
  • Reduce compaction and improve drainage
  • Rotate to corn, wheat to reduce inoculum
  • Reduce plant stress
  • Seed treatments

Sudden Death Syndrome

• Caused by Fusarium virguliforme—only organism that causes SDS in soybeans i.d.
• Favored by cool wet weather soon after planting
• Management:
  • Combination of resistance and seed treatments
  • Improve drainage, avoid compaction
  • Plant into warm soils
  • Manage SCN—when present SDS is worse
  • Use cultivar with moderate resistance to SDS
  • Consider SDS seed treatment (include the base treatment)

Red Crown Rot

• New to Illinois and caused by fungus Calonectria ilicicola
  • Caused ~25 bushel losses in fields present last year
• “Warm season SDS”—flourishes in soils 77-86°F
• Base of plants covered in white mat of fungal growth—center pith of split stem is gray and discolored
  • Typically see in situations where soybeans are rotated with peanuts—typically present in the south, but overwinters here
• Management:
  • Avoid soybean-soybean; rotate to corn, 2 seasons away from legumes optimal
  • Manage residue
  • No available varieties
  • No labeled seed treatments

Summary

• All need saturated soils—drainage management is important
• Rotation is not always a good solution
• Variety resistance, tolerance available for some diseases