As we move through early emergence and stand establishment, crop conditions are often dictated less by what we see above ground and more by what’s happening below the soil surface. Cool, wet conditions across much of the Northern Plains and Upper Midwest can quietly set the stage for early-season disease pressure in both soybeans and yellow field peas.

Understanding what to look for early, along with the conditions that favor disease development, can help guide management decisions and explain variability in emergence and stand.

Soybeans

What to Watch For

1. Seed Decay and Damping-Off (Pythium & Phytophthora)

• Poor or uneven emergence
• Seed rot before emergence or seedlings collapsing shortly after emergence
• Water-soaked, soft tissues on hypocotyls and cotyledons
• Stand gaps, particularly in low or poorly drained areas

These pathogens are among the most common early-season issues and are present in most soils.

2. Seedling Blights (Rhizoctonia & Fusarium)

• Reddish-brown lesions near the soil line (Rhizoctonia)
• Dark brown to black root lesions and reduced root systems (Fusarium)
• Stunted, uneven plants with poor vigor
• Plants that survive but lag behind healthy neighbors

Unlike damping-off, these diseases often allow plants to emerge but reduce early-season growth and competitiveness.

3. Early Foliar Disease Development (Lower Canopy)

• Small brown lesions on lower leaves (Septoria brown spot)
• Angular, water-soaked lesions following early rain events (bacterial blight)

These typically begin in the lower canopy and rarely cause early yield loss but can indicate favorable conditions for disease progression later in the season.

Conditions That Favor Disease

• Cool, wet soils at planting:
  Early planting into soils below ~60°F slows emergence and increases susceptibility to Pythium and Phytophthora.
• Saturated or poorly drained areas:
  Standing water or compaction promotes water mold pathogens and increases infection risk.
• Anything that delays emergence:
  • Soil crusting
  • Deep planting
  • Compaction
  • Herbicide injury
• Residue and continuous soybean systems:
  Residue-borne pathogens (such as Septoria) increase with limited rotation.

Slower emergence extends the window for infection by multiple pathogens.

Yellow Field Peas

What to Watch For

1. Root Rot Complex (Aphanomyces, Fusarium, Pythium, Rhizoctonia)

• Poor emergence and reduced plant stand
• Yellowing and stunting, often starting from the lower canopy
• Browning or rotting of roots and lower stem
• Sloughing or deterioration of root tissue (especially with Aphanomyces)

In peas, early-season disease is typically not caused by a single pathogen but by a complex, making diagnosis and management more challenging.

2. Aphanomyces Root Rot (High Concern in Wet Years)

• Caramel-brown roots with outer tissue sloughing off
• Plants that emerge but remain stunted and yellow
• Premature death in severe cases

This disease is particularly important because it persists in soils long term and is strongly tied to moisture conditions.

3. Early Foliar Diseases (Ascochyta & Bacterial Blight)

• Small dark lesions or flecks on leaves and stems (Ascochyta)
• Water-soaked, angular lesions that turn necrotic (bacterial blight)
• Potential stem lesions that can girdle plants

These diseases can begin early, especially in residue-heavy systems or when infected seed is present.

Conditions That Favor Disease

• Cool, wet soils in early spring:
  The primary driver of pea root rot development, especially Aphanomyces and Pythium.
• Poor drainage and low-lying fields:
  Disease severity often aligns with areas that stay saturated longer.
• Short rotations with peas or lentils:
  Repeated pulse crops increase pathogen levels, particularly for Aphanomyces and Ascochyta.
• Compaction and plant stress:
  Stress weakens seedlings and allows opportunistic pathogens like Fusarium to establish.
• Prolonged leaf wetness or high humidity:
  Drives early foliar disease development such as Ascochyta and bacterial blight.

Key Takeaways

Early-season diseases in both soybeans and yellow field peas are largely driven by environmental conditions at and shortly after planting, particularly temperature and moisture.

• In soybeans, focus on stand establishment issues tied to soilborne pathogens
• In peas, pay close attention to the root rot complex, especially in wet fields or tight rotations
• Across both crops, anything that slows emergence increases disease risk

While in-season rescue options are limited, early scouting and accurate identification help inform:

• Replant decisions
• Variety selection
• Crop rotation planning for future seasons

In short, early-season disease pressure often sets the tone for the rest of the season — and the fields that struggle early are rarely random.