SCN on roots. Photo by Greg Tylka, Iowa State University provided by the SCN Coalition.

Scouting and Sampling for Soybean Cyst Nematode

Adapted from Dr. Anne Dorrance, The Ohio State University

Soybeans are Ohio’s number one cash crop. Soybean Cyst Nematode (SCN) is the number one contributor to yield loss in soybean crops nationwide, causing an estimated $1.2 billion dollars in damage annually. This pest has been detected in 71 counties in Ohio, with the highest concentrations located in the northwestern part of the state.

Locations SCN has been found in Ohio

Significant yield reduction may take place with absolutely no above-ground symptoms. This is one of the main reasons one must sample fields for the presence and abundance of SCN. The quality of the diagnosis (and therefore, the effectiveness of management) is dependent on the method and timing of sampling.

Emerging populations of SCN may have adapted to the resistance found in certain varieties of soybean, rendering the plant susceptible to infection. While not 100% effective, resistant varieties are still providing a reasonable level of reducing or slowing SCN population development.

Now is a good time to scout soybean fields. Symptoms include chlorosis and necrosis. These symptoms occur most often in fields with nutrient deficiencies and/or stressful environmental conditions (such as high temperature and drought), but most of the time no above-ground plant symptoms are visible.

SCN damage on susceptible variety

The cycle of the disease follows the life cycle of the nematode. There are three main life stages of SCN: egg, juvenile, and adult. In Ohio, it is possible to have 3 to 5 generations in one growing season, making timing of sampling important in obtaining correct SCN numbers. SCN samples count the number of eggs in 100 cc of soil and provide a rating based on those findings.

SCN Eggs hatch as second-stage juveniles. These motile roundworms have undergone their first molt inside the egg, emerging at about 1/64 inch long. The juveniles search for soybean roots, most likely using chemical indicators secreted by the soybean root. However, since the juveniles can move only a short distance through the soil before entering the root, they starve to death if no root is found. Water movement within the soil can help the juveniles move farther.

Once a juvenile has found the soybean root, it will penetrate the epidermis and move to the vascular tissue where it will create a feeding site of enlarged cells called a syncytium. The females will become sedentary while the males remain motile.

Once the female is fertilized by the male, it will essentially become an egg-making factory. The body of the female fills with eggs (several hundred of them) and swells, becoming too large to stay within the root tissue. The female bodies become the cysts visible on the outside of the root. These cysts change color as the female ages from white to dark brown.

Some eggs will be deposited from the cyst into a gelatinous matrix, where they may survive for a short period of time before hatching as juveniles. The cyst containing the remaining eggs may then break off of the root and survive in the soil for several years.

As populations of SCN increase, plant symptoms such as chlorosis and necrosis may occur. However, they are not always apparent and yield reductions may still occur.

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