Red crown rot (RCR) of soybean has NOT yet been found in Iowa, but it has cropped up in several neighboring states. RCR is fairly widespread across Illinois and has been identified in Missouri, Wisconsin, and Minnesota (Fig 1). It is likely only a matter of time before RCR is identified in Iowa.
Red crown rot can cause substantial soybean losses, and we are asking farmers and agronomist to be on the lookout for RCR in Iowa fields. To help facilitate this, the Iowa Soybean Association, through the soybean checkoff, is offering free RCR testing for Iowa farmers when samples are sent to the ISU Plant and Insect Diagnostic Clinic.
Red crown rot in a soybean field looks very similar to sudden death syndrome (SDS). Soybean leaves turn yellow and brown between leaf veins and patches of yellowing plants can be viewed from the edge of the field or from overhead (Figs 2 and 3). Leaves eventually wilt and plants may die. However, RCR causes characteristic red discoloration of the lower soybean stem (Fig 4). The fungus that causes RCR can also produce tiny, round, and red fungal structures on the stem and roots near the soil line (Fig 5). Plants with RCR may have extensive root rot (Fig 6).
Key RCR differences compared to SDS:
- Red crown rot causes reddish discoloration on the stem near the soil line. Sudden death syndrome does not.
- Soybeans with RCR can show small, round, and red fungal growths near the soil line on the stem.
- Wilted leaves often remain attached to the stem in plants with RCR. Leaves of plants with SDS fall from the plant while petioles remain.
- Plants with RCR can have greater root rot than those with SDS. RCR can cause “pencil roots” where most of the root system is rotted except a pencil-like portion that still remains.
If you suspect RCR in your fields, please use these guidelines (RCR Sampling Guide.pdf) for preparing a sample for the Plant and Insect Diagnostic Clinic. Samples must be accompanied by a diagnostic clinic submission form, which can be downloaded at https://yardandgarden.extension.iastate.edu/files/inline-files/PIDC45.pdf. Indicate the sample is for RCR.
Confirmation of RCR in Iowa must be verified through a diagnostic laboratory.
This service is provided to Iowa Farmers by the United Soybean Board through the Iowa Soybean Association.
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- Professor
- Extension Plant Pathologist