Plant-parasitic nematodes are microscopic roundworms that can pierce and feed on the roots of soybean and other crops using a special, straw-like apparatus called a stylet. This feeding action causes root damage, which in turn can lead to crop damage and yield loss.

There are numerous different kinds of plant-parasitic nematodes, and in soybean, some are more damaging than others. Typically, across North Carolina, the two most impactful nematodes to soybean production are the soybean cyst nematode (SCN; Heterodera glycines) and the root-knot nematodes (RKN; Meloidogyne spp.), including the Southern root-knot nematode (M. incognita) and the invasive guava root-knot nematode (M. enterolobii). Additionally, in some localized areas, other nematodes that can infect soybeans and limit yields include lesion (Pratylenchus spp.), sting (Belonolaimus spp.), lance (Hoplolaimus spp.), stunt (Tylenchorhynchus spp.), and stubby root (Trichodorus spp.) nematodes. This factsheet will primarily focus on the two major nematode pathogens in soybean (SCN and RKN). However, information is also available for other plant-parasitic nematodes in soybean in the North Carolina Soybean Production Guide.

How then can we keep these invaders at bay and stop them from feasting on soybeans? Managing nematodes is a year-round endeavor, and because of this, the interaction of nematodes with cover crops can play an important role in management.

From the outset, it is important to keep in mind that managing nematodes with a winter cover crop can be difficult. Although researchers here at NC State University and across the U.S. have documented several good non-host winter cover crops to SCN and RKN, the timing of planting a winter cover crop puts most of that cover crop’s growth during the late fall, winter, and early spring months. Here in North Carolina, nematodes are less active and feed less in the cold soils at this time of the year, compared to summer months when the soils are warm. Due to the naturally lower feeding activity in the winter, the effectiveness of a non-host winter cover crop to decrease nematode populations may be less pronounced. However, cover crops can still be a valuable tool in the toolbox of managing nematodes. Let’s take a closer look at benefits and key considerations when using cover crops to manage plant-parasitic nematodes.

1. Certain cover crops can act as a non-host to SCN and RKN, thus providing a break in the “green bridge” between soybean and other susceptible cash crops

The collection of different plants that a nematode can feed upon and complete its life cycle is referred to as the host range of the nematode. If a plant is not within the host range of the nematode, the nematode will not be able to feed or complete its life cycle, and the overall population of the nematode will decrease. Table 1 summarizes the interaction of Southern RKN, guava RKN, and soybean cyst nematode with several winter and summer cover crops.

It is important to note that SCN and RKN can survive for two or more years in the soil even without a host (the nematodes can survive in the egg stage). Planting of a non-host cover crop in the short term is not a complete replacement for crop rotation over several years. Yet, use of cover crops can be a valuable tool to combine with additional nematode management tactics, such as use of resistant varieties, application of a nematicide, and multi-year rotation plans.

* Some studies suggest that unique varieties or cultivars of this cover crop may react differently.

2. Cover crops can suppress weeds, which may be host to SCN and RKN

Many plant-parasitic nematodes can feed on weeds in addition to crop plants. Nematode feeding and reproduction on weeds can contribute to increasing nematode pressure on a soybean crop. Cover crops (provided they are also non-hosts to the nematode of concern) may help to suppress weeds that are host to the nematode of concern. Below, Table 2 summarizes the interaction of Southern RKN, guava RKN, and soybean cyst nematode with weeds common to North Carolina.

You can learn more about suppressing weeds with a Cereal Rye Grass Cover Crop through NC State Extension.

3. Taking advantage of other short-term agronomic benefits that cover crops offer

Cover crops can provide other short-term benefits, such as moisture retention, or adding certain macronutrients and organic matter to the soil. Although these benefits are not directly impacting nematode populations, they may work to reduce stress on a soybean crop that is also challenged by nematode pressure. Additional research is needed to determine the consistency and impact of these effects.

A more thorough discussion and additional information about these benefits can be found in the NC State Extension publication Managing Cereal Rye for Benefits in Cotton and Soybean.

The NCDA&CS Nematode Assay Lab provides soil detection and diagnostics

The NC State University Plant Disease and Insect Clinic provides diagnostic and management recommendations

The NC State Extension Plant Pathology portal provides information on crop disease management

The Southeastern US Vegetable Crop Handbook provides information on vegetable disease management

The North Carolina Agricultural Chemicals Manual provides an up-to-date list of chemicals available for control of nematodes and other diseases and pests

This factsheet was prepared by the NC State University Plant Nematology Lab in 2024. We express gratitude to the NC Soybean Producers Association for supporting cover crop research that contributed to this factsheet (Grant #24-101).