Plant Health Initiative

Sudden Death Syndrome

Figure 1. Scattered yellow spots are the early leaf symptoms of SDS

Figure 2. Late-season foliar symptoms of SDS Click on image to view a larger version

Figure 3. Root rot occurs on plants infected with the SDS pathogen. This symptoms distinguishes SDS from brown stem rot and stem canker. Note the blue discoloration on this sample. Click on image to view a larger version. Photo credit: X.B. Yang, Iowa State University

Foliar symptoms

Symptoms of SDS are fairly easy to recognize. Symptoms first appear as small, bright, pale green to yellow circular spots on the leaves during late vegetative or early reproductive growth stages (Figure 1).

As the disease progresses, the areas between the leaf veins will turn bright yellow, then eventually brown. The dead, brown tissue between veins may die and fall out, leaving large ragged holes and streaks in leaves (Figure 2). Symptoms are generally more pronounced on top leaves. Flowers and pods may abort or not fill.

Root symptoms

A key symptom of SDS is substantial amounts of root rot and discoloration of roots and crown (Figure 3). Diseased plants are easily pulled out of the ground because of decayed lateral roots and taproots. When split lengthwise with a knife, the internal tissue of the main or tap root will be gray to reddish brown, not healthy white.

Symptoms present on both leaves and roots is diagnostic for SDS

SDS may be mistaken for brown stem rot (BSR) and stem canker because these diseases show similar leaf symptoms (see SDS - Scouting). It's important to distinguish between these diseases because the control measures are different:

SDS is diagnosed by the symptoms on both leaves and roots. The outer tissue of SDS- infected stems can be rotted, but the stem’s pith remains white.

Brown stem rot infection results in a distinct brown center (pith) of the stem, but the roots are not affected.

Plants infected with stem canker will develop a brown canker on the main stem. The stems become brittle, but the roots are not affected.

If you suspect SDS, send whole infected soybean plants (tops and roots) to a plant disease clinic for identification.