As reported in the Bulletin (issue no. 19), sudden death syndrome (SDS) on soybeans is beginning to appear around the state. Doug Gucker, in Piatt County, reports finding scattered plants instead of large areas of plants in soybean fields with foliar symptoms characteristic of SDS. Dennis Epplin, in the Mt. Vernon Center, and Omar Koester, in Randolf County, report a little SDS in some areas of soybean fields that were wetter this spring. Robert Bellm reports some SDS appearing in a few fields in southern Illinois. So basically, symptoms of SDS are appearing throughout the entire state. At this time, and it is still a little early, the amount of symptoms being reported seems less than the amount of SDS appearing in fields around this time last year.|
Last year SDS was responsible for approximately $400 million in yield loss. This pathogen typically is more severe during years in which conditions favor optimum soybean growth. Soil moisture is an environmental parameter that influences soybean growth, and the amount of SDS occurring in the field as disease development appears to be favored by high soil moisture or rainfall and irrigation. From this year's reports, SDS symptoms are starting first in fields that received more rainfall this spring.
Symptoms produced by SDS begin as chlorosis and necrosis of the interveinal tissue of leaves, which then coalesce, forming large yellow and brown areas between a green midvein and green lateral veins.
Foliar symptoms of sudden death syndrome on soybeans.
Initially, however, foliar symptoms begin as slight yellow mottling or flecking of the leaf.
Early SDS foliar symptoms.
Other symptoms are rotting of roots, necrosis of the crown, discoloration of the vascular tissue in roots and stems, premature defoliation of the soybean plant, and abortion of the flowers and pods. The effects of root infection are not as apparent, and they can occur without the presence of foliar symptoms.
Infected plants in the field prematurely turn yellow and then brown, whereas healthy plants remain green. Leaves drop off the soybean plant, often from the top, leaving the petiole attached to the stem. The foliar symptoms of SDS seen in the field are similar to those of brown stem rot, but internal symptoms differ in that with SDS there is no pith discoloration.
Vascular discoloration caused by brown stem rot and a healthy root.
Some uniform reddish brown vascular discoloration without a streaking pattern can occur with SDS, but the pith remains white. Leaf symptoms on plants with stem canker can also be confused with SDS; however, soybeans with stem canker have cankers on the lower stem, and plants with SDS do not have cankers.
Cankers on soybean stems.
When observing foliar symptoms that appear to be SDS, be sure to cut open the stem and check for the lack of brown discoloration in the pith. This will ensure that the foliar symptoms are not caused by brown stem root. In addition, check the stem of the plant for the presence or lack of cankers to distinguish the foliar symptoms for stem canker.
This disease is difficult to control in part because infection of the root system occurs in the spring by a soilborne organism and foliar symptoms are not seen until around August. Therefore, it is best to try to manage SDS by lessening the impact of the disease.
1. Learn to identify SDS in the field, as symptoms may appear similar to more common diseases, such as brown stem rot or stem canker.
2. Select soybean varieties that mature at different times. Use either different maturities within a maturity group or different maturity groups. Early-maturing cultivars appear better.
3. Delay planting or extend planting time so that all soybeans are not at the same growth stage at the same time. However, do not wait past the suggested time for your area of the state.
4. Use cultural practices to improve drainage in low spots, reduce cyst nematode populations, and reduce soil compaction.
5. Crop rotation is of limited value because this organism can persist in the soil for many years. However, planting continuous soybeans is not recommended because this can increase other diseases.--Loretta Ortiz-Ribbing