Sudden death syndrome (SDS) generally strikes soybean around the middle of August in Iowa. Because of the unusual weather this growing season, the disease is showing up much earlier and was reported last week from several southern Iowa counties.
The fields that we visited last week had several disease patches in poor drainage areas. Plants in these areas showed intervienal necrosis on leaves and root rot symptoms. The lower portion of stems, when they were split, was gray. In some plants, bluish fungal colonies could be seen on the roots, but these colonies were not as common as in plants later in the summer. Phytophthora root and stem rot also was coexisting with SDS in these fields.
It is well established that the SDS pathogen infects soybean at the seedling stage but symptoms do not occur until the pod-setting stage in Iowa. The early occurrence of the disease this season is interesting and important because it indicates that this pathogen may cause seedling damage. If SDS occurred in your fields in the past few years, keep an eye on your fields this season. In one of the cases reported, SDS was found in the field 2 years ago.
A measure for SDS management is to control the buildup of the pathogen population in soybean fields. If you find the disease, select SDS-tolerant varieties for subsequent soybean plantings. Improve drainage to alter conditions favorable to disease occurrence. The disease often is more severe in no-till fields and use of tillage can reduce the disease incidence.
This article originally appeared on pages 136-137 of the IC-484(18) -- July 17, 2000 issue.