Conditions that favor one type of soybean stem disease often favor many. This is one reason we tend to see increased reports of sudden death syndrome (SDS), brown stem rot (BSR), stem canker, and others all at the same time. These diseases can also be very challenging to distinguish from one another.
Since in-season fungicides are not effective controls for these diseases, why should we care which one we have? Well, knowing your enemy means knowing your control options, and this can make financial sense. Resistant soybean varieties, planting site selection, rotation plans may all be available to help you manage your problem, but only if you know what pathogen you are facing.
Both SDS and BSR are caused by fungi that infect the plant when conditions soon after planting are cool and persistently wet. They both cause identical leaf discoloration that can be very visually striking (Figure 1), and in both cases, symptoms tend to start showing up long after infection, late in the reproductive stages of the plant.
There are some key differences between SDS and BSR that will help you determine which disease your soybeans suffer from.
Scan the affected areas of the field. When they die, do the leaves remain on the plant or fall off? In the case of SDS, leaves will fall off and your plants will look like they were browsed by deer (Figure 2). Plants that hold on to dead, droopy leaves indicate BSR.
Cut open the stems lengthwise. Is there browning of the tissue inside? If browning is found only in the very center of the stem (pith), this indicates BSR. If the browning is not in the center, and instead on either side of the interior of the stem (cortex), you are dealing with SDS (Figure 3).
Pull up some plants and take a look at the exterior of the roots. The pathogen that causes BSR does not affect the roots, only the aboveground plant parts. If you see fuzzy or powdery white or blue growth on the upper portions of the roots, this is indicative of SDS (Figure 4).
The blue color fades with exposure to air, so you will have to look soon after pulling. Opening this root may also reveal brown discoloration.
ASoybean Stem Diseases: What are the Different Symptoms and Signs?Visit the Crop Protection Network Factsheet Library and download “Scouting for Stem Diseases” and “Sudden Death Syndrome” to learn more about these and other soybean stem diseases.with images that may help you further identify and manage these diseases include