Sudden Death Syndrome (SDS) symptoms start simple enough. The light-yellow flecking on the leaves can be easily dismissed as normal dry down. The foliar symptoms don’t typically appear until the plants are well into the reproductive growth stages (July and August).
If the soybean plant is infected by the fungus Fusarium virguliforme that causes SDS, those initial yellow areas will enlarge and you’ll see yellow leaves with the veins remaining green. Eventually, leaves die and turn brown with the veins remaining green.
University of Illinois plant pathologist Carl Bradley says too many growers shrug off the disease because there’s little that can be done this time of year. “Foliar and seed treatment fungicides do not help avoid SDS,” says Bradley. “Management tactics are your best defense.”
Variety selection leads the SDS management chart. “It’s important to identify if you have had problems before the growing season begins,” Bradley notes. “Although no soybean varieties have complete resistance to SDS, differences in susceptibility exist.”
Management practices that improve soil drainage and avoid compaction may also help limit losses.
SDS is also associated with early planting. Bradley recommends planting fields with no history of SDS problems first and finishing with those where you’ve noted SDS in past years. “Observations from the current season indicate soybean fields planted in late April may be affected most by SDS,” he says.
Researchers have also identified some interactions between SDS and Soybean Cyst Nematode. If both are present in the field, yield losses may be more dramatic than if either is present alone.
The leaf symptoms of SDS will be similar to brown stem rot (BSR), Bradley says. You’ll find the differences by splitting the stem. The pith tissue will look normal with SDS and be discolored with BSR.
Although the main SDS symptoms appear on the foliage late in the growing season, the fungus that causes the disease actually infects soybean roots early in the growing season. The foliar symptoms are caused by a toxin produced by the fungus. SDS infected plants will sometimes have a bluish-green discoloration on the surface of the root.
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