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.
![Soybean leaf showing classic symptoms of sudden death syndrome infection, with yellow and brown areas contrasted against a green midvein and green lateral veins.](/content/dam/dpagco/pioneer/na/ca/en/images/articles/IMG-SDS-of-soybeans-1-NA_CA_EN_V1.png)
Figure 1. Soybean leaf showing classic symptoms of sudden death syndrome infection, with yellow and brown areas contrasted against a green midvein and green lateral veins.
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 mid-summer.
- 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.
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.
![Root and stem of soybean plants with blue Fusarium virguliforme fungal colonies present at soil surface line.](/content/dam/dpagco/pioneer/na/ca/en/images/articles/IMG-SDS-of-soybeans-2-NA_CA_EN_V1.png)
Figure 2. Root and stem of soybean plants with blue Fusarium virguliforme fungal colonies present at soil surface line.
- 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.
![Split soybean stem on top shows stem symptoms of sudden death syndrome infection. Split stem on bottom is healthy](/content/dam/dpagco/pioneer/na/ca/en/images/articles/IMG-SDS-of-soybeans-3-NA_CA_EN_V1.png)
Figure 3. Split soybean stem on top shows stem symptoms of sudden death syndrome infection. Split stem on bottom is healthy.
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 infected with sudden death syndrome.](/content/dam/dpagco/pioneer/na/ca/en/images/articles/IMG-SDS-of-soybeans-4-NA_CA_EN_V1.png)
Figure 4. Soybean plants infected with sudden death syndrome. Necrotic areas of leaves dry rapidly. Leaves drop from the plant prematurely, but leaf petioles remain firmly attached to the stem.
![Soybean leaf showing symptoms of sudden death syndrome infection. Drying of necrotic areas can cause curling of affected leave](/content/dam/dpagco/pioneer/na/ca/en/images/articles/IMG-SDS-of-soybeans-5-NA_CA_EN_V1.png)
Figure 5. Soybean leaf showing symptoms of sudden death syndrome infection. Drying of necrotic areas can cause curling of affected leaves
Management
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.
![Soybean leaf showing early symptoms of sudden death syndrome infection](/content/dam/dpagco/pioneer/na/ca/en/images/articles/IMG-SDS-of-soybeans-6-NA_CA_EN_V1.png)
Figure 6. Soybean leaf showing early symptoms of sudden death syndrome infection