Sudden Death Syndrome (SDS) in Soybeans – Are we at risk this year?
Aug 16Sudden Death Syndrome (SDS) in Soybeans – Are we at risk this year?
SDS is a soil-bourne fungal pathogen, Fusarium solani, which infects roots shortly after planting. Above-ground symptoms (yellow, irregular mottling between veins on upper leaves) caused by a toxin will usually not appear until after flowering. Eventually, leaves will become necrotic and fall, leaving petioles attached to the stem. To distinguish between other root rots (brown stem rot), the pith remains white in SDS plants, but you may see some discolouration in the vascular tissue.
SDS can survive between soybean crops as chlamydospores in crop residue and soil for long periods of time, which usually causes infected areas to increase over time. In the spring, spores near the soybean roots are stimulated to germinate and infect. If early spring conditions are favourable for rapid plant growth and there are no big rains, the risk of SDS lowers.
This year, some areas have had ideal conditions for disease development; heavy rains during reproductive stages, cool wet soils, early planting, high moisture and soybean cyst nematode (SCN).
What can you do? SDS is commonly more severe where SCN is present, therefore, management practices that help control SCN may reduce your risk of SDS. If you have a history of SDS in your field, address any drainage issues and plant it last with a tolerant variety.
Foliar fungicides will not work to control SDS because the fungus that causes the toxins are in the root system and fungicides do not move to the roots. Yield impacts are greatly determined by the severity and timing of the disease. If SDS develops early, flowers and young pods will abort; later infection causes fewer seeds per pod and smaller seeds.
Laura Johnston, CCA-ON, Maizex Seeds Yield Specialist, West Elgin County