Sudden Death Syndrome
Sudden Death Syndrome (SDS) has recently been found in 5 counties in South Dakota. SDS of soybean is a fungal disease that attacks soybeans early in the growing season, but symptoms suddenly appear during the flowering and reproductive growth stages through pod fill. Plants that looked perfectly normal can turn yellow and die in a very sudden and short time frame (1 to 2 weeks), hence the name.
Detection of SDS
SDS causes symptoms on both roots and foliage. On foliage, symptoms of SDS first appear as small, pale green, circular spots on leaves during the early reproductive growth stages. These spots enlarge into striking/flashy yellow irregular blotches between veins while the veins remain green. The yellowed blotches turn brown and die. In severe cases, the leaves drop prematurely leaving the petioles attached to the stem. Infected plants may not always show foliar symptoms.
Roots of a soybean plant infected with SDS are rotted and discolored. Diseased plants can easily be pulled out of the ground because of rotted lateral roots. If the plants are pulled when the soil is moist; small, light-blue patches can be seen on the surface of the taproot. When the taproot of the infected plant is split lengthwise, the internal tissue will be gray to brown, as opposed to the normal cream white color of a healthy plant.
Management of SDS
SDS is difficult to manage, and by the time symptoms are seen there is little that can be done to manage the disease. Seed treatments have not been found effective and foliar fungicides do not protect soybean from SDS infection. It is important that growers scout their fields, send samples suspected to have SDS to the Plant Diagnostic Clinic at SDSU and keep notes on the history of SDS in their fields. Testing for SDS is provided free of charge to growers, thanks to the support of the South Dakota Soybean Research and Promotion Council.
Fortunately, there are a number of management strategies that can lessen the impact of SDS on soybean yield. If SDS is confirmed in the field, use soybean cultivars that are SDS resistant or SDS tolerant. Seed companies provide disease ratings for SDS. Planting should be done in warm and well-drained soils. Wet and cool soils promote SDS pathogen infection. SDS is commonly found in plants that are also infected with the soybean cyst nematode. Therefore managing the soybean cyst nematode may reduce chances of SDS infection. Because the SDS pathogen can survive on corn kernels, clean corn harvesting is encouraged.