Figure 1. Distribution of sudden death syndrome on a soybean plant. Note the green veins in leaves and more damage to the upper part of the plant first.

August 24, 2007

Sudden Death Syndrome (SDS) has been found in many Nebraska soybean fields over the last two weeks. This disease was only first confirmed in the state in 2004. Calls and samples across the eastern half of Nebraska suggest the disease is widespread, but in most fields large areas are not affected.

Sudden death syndrome of soybean is caused by the fungus Fusarium solani f. sp. glycines (Figure 1). This is a different fungus than the one which caused early season damping off problems associated with soybean stand. This year's weather with moisture early season and at the early reproductive stage has been conducive to SDS. You should be able to see full symptom expression now.

Early planting favors SDS. With all the information on increasing yields with earlier planting, we expect to see more of this disease. Soil compaction and high fertility levels also have been associated with increased levels of SDS. The foliar symptoms start with interveinal necrosis and the spots coalesce to form brown streaks between the leaf veins with yellow margins. Leaves eventually drop with petiole (leaf stem) remaining attached. The root system will have a deteriorated tap-root and lateral roots will only be evident in the upper soil profile. The root cortex is light-gray to brown and may extend up the stem. Typically plants can be pulled from the ground easily and will have a dark blue fungal growth on the roots. The blue color will not be evident in dry soil conditions.

At this time SDS appears to be widespread in Nebraska, but it can be effectively managed. If a large area of the field is affected, avoid early planting and use resistant varieties next year. Thus far, seed treatment has not been shown to be effective.

Loren J. Giesler
Extension Plant Pathologist