Brown stem rot is a common soybean disease in the north central U.S. that can cut yields up to 15%.1 It’s one of a trifecta of associated conditions you should monitor carefully — the others being soybean cyst nematode (SCN), which can compound yield harm caused by brown stem rot, and sudden death syndrome (SDS), with which brown stem rot shares key symptoms.
Keeping a watchful eye out for these conditions can help you maintain crop health and protect your bottom line.
How to scout for brown stem rot in soybeans
Understanding what brown stem rot in soybeans looks like and knowing when to monitor most closely can help you keep your crop in check.
When to inspect brown stem rot in soybeans
Start scouting for brown stem rot when pods are full from R4 to R5 growth stages.2
If pods fill during cool and wet weather and conditions turn hot and dry by mid- to late August, you’ve got a prime environment for brown stem rot. The disease arises from a fungus called Cadophora gregata that lives in the soil and on crop residue.
Brown stem rot in soybeans begins by infecting the plant at the roots, moving into the stem at vegetative and early reproductive stages.
Symptoms of brown stem rot in soybeans
If you find some of these symptoms confusing, you’re not alone. Brown stem rot is often mistaken for something else, such as an early maturing crop, the byproduct of dry soils or other diseases.3 Avoid the confusion by looking for these telltale signs:
Stem discoloration
Examine several soybean stems by cutting them lengthwise. If the pith is a chocolate-brown color, especially along nodes close to the soil surface, brown stem rot could be the culprit. In fact, some plants never show foliar symptoms, so always start with a stem cross-section.4
Leaf problems
Although not all plants experience leaf problems, you might see yellow or brown tissue between leaf veins, also known as interveinal chlorosis or necrosis.5 These symptoms typically emerge at R5 and peak at R7, especially when lower-than-normal air temperatures have been present. If the disease persists, leaves can wilt and curl, which can signal the highest levels of yield loss associated with brown stem rot in soybeans.
A common disease often mistaken for brown stem rot is SDS. Help prevent misdiagnosis by familiarizing yourself with the commonly confused symptoms of these diseases.
Differentiating brown stem rot from sudden death syndrome
How to distinguish between actual brown stem rot and SDS
Although above-ground conditions are identical for these diseases, it’s pretty easy to tell the difference between the two by examining roots and stems:
- Roots: Brown stem rot roots appear healthy, whereas those affected by SDS appear rotted.
- Stem: Brown stem rot causes the pith of stems to turn a brownish color, whereas soybeans with SDS have pith that’s white and appears healthy.
Brown stem rot and soybean cyst nematode
In addition to differentiating between brown stem rot and SDS, it’s important to keep an eye out for soybean cyst nematode symptoms, too. Soybean cyst nematode can compound the negative, yield-damaging effects of brown stem rot because it weakens the soybean plant and limits its ability to fight disease.
How to manage brown stem rot in soybeans
There are several proactive measures you can take to mitigate the risk of brown stem rot:
Plant different varieties
Although brown stem rot resistance is a moving target, it’s a good idea to rotate the soybean varieties you plant to capitalize on any resistance benefits and also on maturity advantages. For example, plants that mature earlier in the season might incur less yield damage than varieties that mature later.
Manage crop residue
Tillage can push old crop stubble beneath the soil, encouraging decomposition and limiting the risk of brown stem rot in future soybean crops.6
Rotate soybeans with other crops
If brown stem rot is particularly widespread in a field, you should avoid planting soybeans there for two to three years to get the fungus under control. In less severe cases, a corn-soybean or small grains-soybean rotation can help break the disease cycle.
Explore soil amendments
Brown stem rot isn’t fazed by foliar fungicides or seed treatment fungicides. Infection can persist after a seed treatment dissipates. A better approach to mitigating the risk of brown stem rot at the soil level is to keep soil pH at 7, which can be done with a soil amendment such as lime.7
Brown stem rot soybean wrap-up: a preventable disease
By scouting at the right time and monitoring triggering environmental conditions, you can spot brown stem rot and manage it proactively ahead of the next growing season.
Experts are available to help you make your proactive soybean management decisions. Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative.
________________________________________________
Endnotes
- University of Minnesota Extension. “Brown Stem Rot (BSR) of Soybean.” Extension.umn.edu, Regents of the University of Minnesota, https://extension.umn.edu/soybean-pest-management/brown-stem-rot-bsr-soybean. Accessed 7 Apr. 2025.
- Soybean Research & Information Initiative. “Brown Stem Rot.” Soybean Research & Information Network, https://soybeanresearchinfo.com/soybean-disease/brown-stem-rot/. Accessed 7 Apr. 2025.
- University of Nebraska–Lincoln. “Brown Stem Rot.” CropWatch, Institute of Agriculture and Natural Resources, https://cropwatch.unl.edu/plant-disease/soybean/brown-stem-rot/. Accessed 7 Apr. 2025.
- Crop Protection Network. “Brown Stem Rot of Soybean.” Crop Protection Network, https://cropprotectionnetwork.org/encyclopedia/brown-stem-rot-of-soybean. Accessed 7 Apr. 2025.
- Doll, Jim, et al. Brown Stem Rot of Soybean. University of Wisconsin Extension and University of Wisconsin Plant Pathology, Apr. 2013, https://badgercropdoc.com/files/2013/04/Brown-Stem-Rot-of-Soybean.pdf. Accessed 7 Apr. 2025.
- Wise, Kiersten A., and Carl A. Bradley. Brown Stem Rot of Soybean. Purdue Extension, BP-41-W, https://www.extension.purdue.edu/extmedia/BP/BP-41-W.pdf. Accessed 7 Apr. 2025.
- “Soil Amendments: Pros, Cons for Corn, Soybean Farmers.” AgWeb, 22 Apr. 2024, https://www.agweb.com/news/crops/soil-amendments-pros-cons-corn-soybean#:~:text=corn%20and%20soybeans-,Lime,and%20potentially%20changing%20soil%20structure.
