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:

--Carl A. Bradley

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