Soybean Cyst and Root Knot Nematodes

Nathan Kleczewski, Extension Specialist – Plant Pathology;

This year has thus far been excellent for soybeans in the region. With outstanding crop growth comes large, lush canopies that require a substantial amount of water and nutrients to meet the physiological demands of the plant. When the water and nutrient requirements for beans are high and water availability is low, root related issues tend to become more pronounced. This has been the case in some dryland fields in the region where aboveground symptoms of soybean cyst (SCN) or root knot (RKN) nematode are starting to appear. These nematodes reduce translocation of water and nutrients from roots to foliage by compromising the root system.

What do these symptoms look like from afar? You might notice yellowing of foliage in portions of the field, particularly raised, well drained areas (Fig. 1). In some cases you may notice plants are stunted to various degrees. To determine if SCN or RKN might be involved, use a shovel to dig up symptomatic plants. Carefully knock off as much soil as possible and examine the root system. SCN appears as small yellow or white lemon-shaped bumps on the roots (Fig. 2). These bumps are much smaller than nodules formed by nitrogen fixing bacteria which also will be present on the root. If RKN is present you will notice larger, irregularly formed growths on the root system (Fig. 3). The irregular shape and lack of a pink internal coloration further distinguish them from bacterial nodules. It’s always a good idea to look at healthy plants for a comparison whenever possible.


Figure 1. Symptoms of nematode damage on soybean from afar. Symptoms may resemble several other biotic or abiotic issues. Photo by E. Sikora obtained from with permission.


Figure 2. Small, white, lemon-shaped cysts from soybean cyst nematode. Photo by P. Bachi obtained from with permission.


Figure 3. Large, irregular galls caused by Root knot nematode activity on soybean roots. Photo by E. Sikora obtained from with permission.