Brown Stem Rot - Scouting

Cut stems longitudinally in several places at full pod stage to check for internal browning (left), compared to white healthy stem (right).
Photo credit: Dean Malvick, University of Minnesota

Recognizing brown stem rot isn't easy. Symptoms are usually not evident until late in the growing season, and are often confused with early crop maturity or the effect of dry soils. 

At the full pod stage, cut stems longitudinally in several places, and check for a chocolate-brown discoloration in the pith, especially at and between nodes near the soil line. Initially the discoloration may only be found at the nodes, but it becomes continuous through the stem as the plant ages and cool temperatures prevail. 

BSR often causes only internal stem browning and a general mild necrosis, wilting or premature maturation and defoliation of infected plants. Foliar symptoms (browning between the leaf veins) are seen only sporadically. 

Look-alikes

Brown stem rot can be mistaken for sudden death syndrome or stem canker because these diseases cause similar leaf symptoms. However, root and stem symptoms differ among the three diseases.

 

Table 1. Comparison of the signs and symptoms of brown stem rot, sudden death syndrome, stem canker.

Plant Part
BSR
Stem Canker
SDS
Roots

healthy

healthy

root rot

Exterior stem

healthy

dark, reddish-brown sunken canker starting at node

healthy

Interior stem

brown pith (center)

slight browning at nodes to completely deteriorated stems

white, healthy pith
Leaves

no symptoms
or
yellowing between veins

general yellowing of leaves

yellowing between veins similar to BSR

 

Adapted from: Agronomy Guide for Field Crops (Soybeans: Brown Stem Rot, Stem Canker and SDS)
Ontario Ministry of Food and Agriculture.

 

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