Sudden Death Syndrome Observed in Soybean Fields in Southwestern Ontario

Dr. Rishi Burlakoti
Weather INnovations Consulting LP, Chatham

Sudden death syndrome (SDS), a widespread soil-borne disease in Ontario, was observed last week in soybean fields in southwest Ontario. The disease is caused by the fungus Fusarium vilguliformis. The fungus survives in crop residues and soil for several years. The fungus infects soybean plants in its early stages, however, the symptoms do not appear before late flowering to early pod filling. The probability of SDS incidence is high in fields infested with soybean cyst nematodes.

How to Identify Sudden death syndrome?

Death Syndrome
Foliar symptoms: Scattered yellow spots occur initially between veins in soybean foliage. Once the disease progresses, the spots change to yellow and brown blotches between the leaf veins, but mid veins and lateral veins remain green (Fig. 1). In advance stages of disease, the entire plant wilts. SDS symptoms appear in patches in the fields where soil moisture and compaction is high. The foliar symptoms of SDS and brown stem rot (BSR) are similar; however, the symptoms between them can be distinguished by observing the internal stem. The pith of stem is white in SDS infected plants, whereas BSR infected plants produce brown discoloration in the pith.

Symptoms in roots: Root rots are observed in infected plants. When the woody tissue of tap root and stem near ground cut longitudinally, light gray to brown discoloration is observed (Fig. 2).

Death Syndrome
Impact of Weather and Management Strategies:High rainfall during late vegetative to early pods filling (R4-R5) stages favors the incidences of sudden death syndrome in soybean. Frequent and high amount of rainfall occurred in these periods in southwest Ontario (Fig. 3) making a favourable environment for the disease development. The disease incidences are high in poorly drained fields with compacted soil.

Death Syndrome
Foliar fungicides are not very effective to control the disease since the SDS pathogens enter to the plants through roots and grow systemically to the entire plant. Integrated disease management strategies can be deployed for sustainable management of the disease. These practices include: use of seed treatment chemicals, cultivation of tolerant cultivars, crop rotation with non-host crops, proper drainage in fields and improving soil health with proper fertilizations and cultural practices.

Source: Weathercentral