Sudden death syndrome (SDS) in soybeans is a tough critter to control. Getting a handle on this disease takes a full management approach.
SDS occurs in a disease complex with soybean cyst nematode. It is second only to cyst nematode as the most devastating soilborne problem of soybean in the United States. When this disease occurs in the presence of cyst nematode, symptoms occur earlier and are more severe. SDS is typically not detectable on the foliage of plants until after they begin flowering. The fungus infects seedling roots soon after planting. Above ground symptoms rarely appear before mid-July when the fungus penetrates the plant’s vascular tissue. The fungus produces toxins in the roots that are translocated to the leaves and cause foliar symptoms. The fungus itself does not invade the stems more than a few centimeters above the soil line.
Early planting predisposes soybean to SDS infection. In cool, wet soils, young soybean plants are vulnerable to infection by the SDS causal fungus. Avoid early spring planting in soils not favorable for rapid soybean growth. Fields with no history of SDS should be planted first; fields where SDS has been a problem should be planted later.
Cyst nematode injures seedling plants, which makes them more vulnerable to SDS. Begin SDS management with nematicides active against cyst nematode and/or resistant varieties. Nematicides, including some biological products, should be used before you consider using an additional seed treatment fungicide directed at SDS. Fungicides in-furrow or foliar-applied are not effective on SDS.
Resistance management options to control SDS are limited. Although soybean cultivars less susceptible to SDS have been developed, no highly-resistant varieties are available. Nonetheless, you may get the biggest bang for your buck by starting with a nematicide in combination with a variety that has some level of SDS resistance.
A few technologies are available for SDS fungal control. ILeVO seems to be the most effective against the SDS causal agent and has activity on cyst nematode as well. Thiabendazole (TBZ) may help at high application rates. While it is too early to know how well Heads Up will perform, limited results have been promising.
The bottom line: Plant later to manage SDS. When that is not an option, use a nematicide alone or in combination with a variety that has some SDS resistance. If the problem is severe, add a fungicide directed at SDS.