First detection of SDS in South Dakota
Signs and Symptoms of Sudden Death Syndrome
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," Byamukama said.
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 tap root 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.
Scout fields and send suspect plants in for testing
SDS, being a soil-borne pathogen, is difficult to manage and by the time symptoms are seen, there is little that can be done to manage the disease, Byamukama said.
"Seed treatments have not been found effective and foliar fungicides do not protect soybean from SDS infection. It is therefore important that growers scout their fields," he said.
If SDS issue is suspected, Byamukama said South Dakota growers should send samples to the Plant Diagnostic Clinic at SDSU at no grower cost, thanks to a grant from South Dakota Soybean Research and Promotion Council. Other state’s growers should also confirm SDS with clinical testing in their state, and ag retailers can be a big help to assist these growers in identification and sampling for testing. Byamukama also encourages growers to keep notes on the history of SDS in their fields.
Management Practices for SDS
Fortunately there are a number of management strategies in place 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," Byamukama said.
Seed companies provide disease ratings for SDS, growers should check for SDS rating, once SDS has been confirmed in their fields. Planting should be 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.