Since it was first observed 26 years ago in the Chatham area of Ontario, Soybean Sudden Death Syndrome (SDS) has emerged as a persistent and increasing yield-limiting problem for eastern Canadian soybean growers. SDS infections can occur across most soybeans grown in this region. Yield loss is highly variable and is influenced by the severity of initial infection, seed product susceptibility, subsequent weather conditions, and soybean cyst nematode (SCN) populations. Moderate disease pressure can result in yield losses from 10 to 20 percent and up to 50 percent under severe disease pressure.¹ Losses of 100 percent in some fields have been reported. The disease is well established in Southern Ontario, and according to recent disease survey data, is most severe in Chatham, Elgin, Norfolk and Essex counties.² The disease has been reported recently in Middlesex, North London, and Perth as well.^2,3

SDS Disease Cycle and Symptoms

Sudden Death Syndrome is caused by the soilborne fungus Fusarium virguliforme. The fungus overwinters in crop residue or soils. Infection can occur soon after planting, but above-ground symptoms usually appear after flowering and during pod-fill. SDS is favored by high-yield environments, cool and wet weather after planting, and compacted soils. In addition, moderate to high populations of soybean cyst nematode (SCN) can be associated with SDS and may increase the severity of the disease.

Foliar Symptoms: The late-season foliar symptoms appear as yellow, chlorotic blotches that form between soybean leaflet veins. The blotches expand into large, irregular, chlorotic patches that become brown and eventually die. Leaflets are likely to drop off the plant leaving the petiole attached to the stem (Figure 1). Plants infected with SDS are likely to abort flowers and pods.

Stem and Root Symptoms: Soybean stem canker (northern and southern) and brown stem rot (BSR), cause foliar symptoms similar to those of SDS. To differentiate between the symptoms of these other diseases and SDS, it is important to dig up plants, inspect roots closely, and split soybeans stems lengthwise. Upon inspection, the pith of plants infected with SDS will be white, although the cortex may show brown to gray discoloration (Figure 2). On occasion, the roots may exhibit bluish-white spore masses (Figure 3). In contrast, the pith of BSR-infected plants becomes tan to brown near the crown and stem nodes (Figure 4).

If any uncertainty remains after field inspection, do not hesitate to have a laboratory diagnosis done to confirm the presence of SDS or to diagnose the cause of the observable symptoms.

Management

Yield losses from SDS range from slight to nearly 100% and are dependent on disease onset and severity. Managing for SDS should occur prior to planting with practices that can help reduce the potential for infection:

• Product selection is a critical management tool for SDS. Soybean products should be reviewed and selected based on SDS and SCN tolerance and resistance levels.
• Reducing SCN population densities with the use of SCN-resistant varieties and crop rotations may reduce the risk of SDS.
• Seed should be treated with a fungicidal seed treatment. Foliar fungicides have not been effective because fungal infection occurs in the root system.
• Consideration should be given to improving field drainage through tiles or field leveling.
• Soil compaction should be addressed with appropriate deep tillage and management practices that reduce the potential for creating compaction.
• Earlier maturing products may reduce disease impact.
• Consider planting later in the season when soils may be drier and warmer.