Sudden Death Syndrome

By Dylan Mangel, Extension Plant Pathologist

Pathogen

Sudden Death Syndrome (SDS) is caused by the soilborne fungus Fusarium virguliforme. This fungus overwinters in residue and in soil as chlamydospores, which are durable survival spores (similar to oospores of Phytophthora spp.) Foliar symptoms are caused by toxin(s) produced by the fungus, which are translocated to the foliage from infected root and crown tissue.

Disease Symptoms

Foliar symptoms of sudden death syndrome typically do not appear prior to soybean flowering. Early symptoms at the R3 and later growth stages consist of the presence of chlorotic (yellow) spots on the leaves between veins. As the symptoms advance, the yellow spots may coalesce but stay between the veins at the leaf margin. Eventually, the yellow areas between the veins will become brown (necrotic) as the tissue dies.

Roots will exhibit a root rot on the tap root. The discoloration of the vascular tissue is contained to the outer stem area (xylem vessels) and can extend up the stem from the soil line. The pith will remain white. (This is a key symptom to differentiate SDS from brown stem rot.)

Pods may be aborted and plants may defoliate early. Defoliated plants will retain their petioles (leaf stems). Retention of the petioles is a symptom frequently associated with SDS.

Symptoms on the root system are difficult to distinguish from other soybean root rots. When roots are removed from soil, the fungus is sometimes visible on the outer root surface. In some rare cases, this fungal growth will be blue.

Sudden Death Syndrome field — SDS Symptoms differ between tolerant varieties and susceptible varieties. There are four rows of a tolerant variety planted between two susceptible varieties. (Photo by Dylan Mangel, Nebraska Extension)

Fungus on root — Blue growth of the Fusarium virguliforme fungus growing on soybean roots. This blue growth is rarely found on SDS infected plants in Nebraksa. (Photo by Dylan Mangel, Nebraska Extension)

SDS-infected plants — A pocket of SDS infected plants in a demonstration plot. (Photo by Dylan Mangel, Nebraska Extension)

Foliar symptoms on leaf — Foliar symptoms of plants infected with sudden death syndrome. (Photo by Dylan Mangel, Nebraska Extension)

Favorable Environmental Conditions

Sudden Death Syndrome is favored in high-yield environments. The disease is more prevalent during cool, wet growing seasons and is favored by early planting in cool soils. Hot, dry weather appears to slow disease development, but depending on the stage and infections — which may have occurred prior to dry weather — it can become severe under these conditions. Heavy rains around the flowering time promote foliar symptom development.

Management

Genetic Resistance

Soybean varieties with moderate to high levels of resistance to SDS are available. Varieties with partial resistance or tolerance to SDS should be considered in fields known to be affected by this disease. These varieties will not prevent disease completely, but they can protect yield.

Cultural Practices

Avoid early planting in fields know to be severely affected by SDS. Two-year rotation out of soybean production and maintaining good crop nutrition has been shown to reduce the severity of SDS.

Chemical/Biological Control

There are chemical seed treatments that provide protection against sudden death syndrome. Find up to date efficacy information on product performance at the crop protection network or in the Extension Guide for Weed, Disease, and Insect Management in Nebraska (EC130).