Wet Weather Blight (Soybean) (commonly caused by fungi like Phytophthora sojae infection or similar pathogens) is a disease favored by excessive moisture.

• Leaves develop water-soaked spots that turn brown and necrotic

• Infected leaves may rot, collapse, and stick together

• Stems can show dark lesions and soft rot

• Plants appear wilted even in moist soil

• Severe cases lead to rapid plant death in patches

Conditions:

• Common in continuous rain, waterlogged, and poorly drained soils

• Spreads quickly in high humidity and standing water

Management:

• Ensure proper field drainage

• Avoid water stagnation

• Use resistant varieties

• Practice crop rotation

• Treat seeds with recommended fungicides

Sudden Death Syndrome (SDS) – Soybean (caused by the soil-borne fungus Fusarium virguliforme infection) is a major root and foliar disease.

• Leaves show yellowing between veins (interveinal chlorosis)

• Affected areas turn brown and necrotic, while veins remain green

• Leaves may dry and fall off, leaving petioles attached

• Roots show rot and discoloration, reducing nutrient uptake

• Stem interior remains white, but outer tissues may be affected

• Plants may suddenly wilt and die, especially during pod filling stage

Conditions:

• Common in cool, wet soils early in the season

• Symptoms become severe during warm and dry conditions later

Management:

• Use resistant varieties

• Improve soil drainage

• Avoid early planting in cold, wet soils

• Practice crop rotation

• Maintain overall soil health

Bud Blight (Soybean) (caused by the virus Tobacco streak virus infection) is a serious viral disease affecting growing points.

• Buds and young leaves show necrosis (drying and death)

• Top shoots become brown, dry, and die (blighting of buds)

• Leaves may show yellowing and distorted growth

• Pods can develop brown spots and poor seed filling

• Plants become stunted with reduced yield

Conditions:

• Spread mainly by thrips (insect vectors)

• Also associated with infected plant debris and weeds

Management:

• Control thrips population

• Remove and destroy infected plants

• Maintain weed-free fields

• Use healthy seeds and resistant varieties

Target Spot (Soybean) (caused by the fungus Corynespora cassiicola infection) is a common foliar disease.

• Leaves show round brown spots with concentric rings (target-like pattern)

• Spots may have yellow halos around lesions

• Lesions enlarge and merge, causing leaf blight

• Severe infection leads to yellowing and premature leaf drop

• Can also affect stems and pods

Conditions:

• Common in warm, humid weather

• Spreads through rain splash and infected crop residue

Management:

• Use resistant varieties

• Practice crop rotation

• Maintain proper field sanitation

• Apply fungicides if necessary

Rhizoctonia Aerial Blight / Web Blight (Soybean) (caused by the fungus Rhizoctonia solani infection) affects leaves, stems, and canopy.

• Leaves develop irregular brown lesions that quickly enlarge

• Infected areas show web-like fungal growth (mycelium)

• Leaves stick together, forming blighted patches in canopy

• Severe infection causes leaf blight, drying, and defoliation

• Can also affect stems and pods

Conditions:

• Common in warm, humid weather with dense crop canopy

• Spreads rapidly through contact between plants and moisture

Management:

• Maintain proper plant spacing for airflow

• Avoid excess irrigation and water stagnation

• Practice crop rotation

• Apply fungicides when needed

Powdery Mildew (Soybean) (caused by the fungus Erysiphe diffusa infection) is a common foliar disease.

• Appears as white powdery growth on leaves, stems, and pods
• Infected leaves may turn yellow and dry
• Severe infection leads to premature leaf drop
• Pods may be affected, causing poor seed development
• Reduces photosynthesis and yield

Conditions:

• Common in cool to moderate temperatures with high humidity
• Does not require free water to spread (unlike many other fungi)

Management:

• Use resistant varieties
• Maintain proper plant spacing for airflow
• Avoid excess nitrogen fertilizer
• Apply fungicides if disease is severe

Frog Eye Leaf Spot (Soybean) (caused by the fungus Cercospora sojina infection) is a common foliar disease.

• Shows circular spots with light grey centers and dark reddish-brown borders

• Spots resemble a frog’s eye pattern

• Severe infection causes leaf yellowing and early leaf drop

• Can also infect stems and pods

• Leads to reduced photosynthesis and yield loss

Conditions:

• Common in warm, humid weather

• Spreads through infected crop residue and seeds

Management:

• Use resistant varieties

• Practice crop rotation

• Remove infected plant debris

• Apply fungicides if needed

Cercospora Leaf Blight, Leaf Spot & Purple Seed Stain (Soybean) are related diseases caused by the fungus Cercospora kikuchii infection.

Symptoms:

• Leaf Blight:
  • Upper leaves show bronze to purple discoloration
  • Leaves may become leathery and dry
• Leaf Spot:
  • Small reddish-brown to dark spots on leaves
  • Spots may merge, causing leaf damage and drying
• Purple Seed Stain:
  • Seeds develop purple discoloration
  • Reduces seed quality and market value

Other Effects:

• Can cause early leaf drop
• Reduces photosynthesis and yield
• Infection often starts late in the growing season

Conditions:

• Common in warm, humid weather
• Spreads through infected seeds and crop residues

Management:

• Use disease-free seeds
• Follow crop rotation
• Apply fungicides when necessary
• Maintain field sanitation

Alternaria Leaf Spot (Soybean) (caused by the fungus Alternaria alternata infection) mainly affects leaves.

• Shows small to large brown spots with concentric rings (target-like pattern)
• Spots may have yellow halos around lesions
• Leaves turn yellow and may drop early
• Severe infection reduces photosynthesis and yield
• Can also affect pods in advanced stages

Common in warm, humid conditions with high moisture.

Crop rotation, field sanitation, and fungicide application help manage the disease.