Issue No. 18, Article 4/August 6, 2010
Sudden Death Syndrome Being Observed in Illinois
Symptoms of sudden death syndrome of soybean (SDS, caused by the fungus Fusarium virguliforme) are being observed in some Illinois fields. Initial symptoms appear as light-yellow flecking on the leaves. The yellow areas enlarge to cause interveinal chlorosis (yellow leaves with the veins remaining green) and eventually interveinal necrosis (dead leaves with the veins remaining green). These foliar symptoms generally do not appear until the soybean plants are into the reproductive growth stages (July and August).
Foliar symptoms of sudden death syndrome on soybean.
Although SDS symptoms appear on plant foliage, the Fusarium fungus that causes the disease actually infects soybean roots early in the growing season. The foliar symptoms are caused by a toxin produced by the fungus, which moves upward in the vascular system of the plant.
Soybean plants affected by brown stem rot (BSR, another important disease in Illinois) have foliar symptoms identical to those caused by SDS. It is important to determine which disease is present, which can be done by splitting the stems of symptomatic plants and observing the pith tissue. If the pith tissue is discolored, then BSR is likely the disease; if the pith tissue is not discolored, then SDS is likely the disease.
Unfortunately, there are no silver bullets available to control SDS completely, so using multiple management practices is encouraged to help limit its damage. Foliar and seed treatment fungicides do not affect SDS. The management tactics outlined here can be used to limit the severity and impact of SDS:
- Variety choice. One of the most important SDS management decisions can be made before the growing season begins. Although there are no soybean varieties with complete resistance to SDS, differences in susceptibility do exist. Many seed companies provide SDS-resistance ratings for their soybean varieties. Also, many soybean varieties are rated for SDS by University of Illinois, Southern Illinois University, and USDA-ARS personnel in field and greenhouse trials as part of the Illinois VIPS (Varietal Information Program for Soybeans). The results of these trials are available at www.vipsoybeans.org.
- Planting date. Early planting may predispose soybean plants to infection by the SDS fungus. Plant fields with no history of SDS first and those with a history of SDS last. Thus far, observations from the current season indicate that soybean fields planted in late April may be affected the most by SDS.
- Soil compaction and drainage. Soils with compaction and/or drainage problems may lead to bigger problems with SDS. Management practices that alleviate a field's soil compaction and drainage difficulties may also help limit losses from SDS.
- Interaction with soybean cyst nematode. There appears to be an interaction between SDS and the soybean cyst nematode, although it is not necessarily easy to prove in research trials. If both are present in a field, then yield losses may be more dramatic than if either is present alone. Good management practices for SCN will certainly reduce related losses, and they may also provide some benefits with SDS management.
--Carl A. Bradley
Carl A. Bradley