Typically, soybeans may begin to show symptoms of soybean cyst nematode (SCN) damage by July 1st. SCN is a parasitic roundworm that feeds on the soybean root system. The cyst stage of the nematode’s life cycle is when the female nematode is filled with eggs. Cysts are visible throughout the summer on soybean roots and will appear as small, white, and lemon-shaped. After the female matures, these cysts are hard to see. When trying to identify SCN presence on soybean roots, it is important not to confuse cysts with Rhizobium nodules (where N fixation takes place).
How can you determine if SCN is causing damage and yield loss to your soybeans? Injury symptoms include yellowing and stunting of plants. These symptoms may appear in patches of a field. These patches may grow from year to year; especially in the direction a field is tilled. Symptoms may become worse when plants are under other stresses in addition to SCN injury and can be confused with other issues, such as nutrient deficiencies. Soil in fields where SCN damage is suspected should be sampled and sent to a lab for analysis. The population level of SCN will determine the specific practices required to manage the problem.
Depending on the population level and the amount of damage being done, growers will have a few management options to consider. Planting soybean varieties with resistance to SCN is critical in fields where the parasite is present. Rotation away from soybeans to a non-host crop (such as corn) can also lessen the amount of SCN injury. In high population fields growers should rotate to a non-host crop for multiple years. It is also important to effectively control weeds, some of which can be SCN hosts as well. For more information and to see a list of SCN host plants, click here.