Soybean Cyst Nematode: The Most Yield Constraining Pest in Soybean Production

Soybean cyst nematode (SCN) is a destructive pest that plagues the booming soybean industry. Since 1950, U.S. soybean production has increased sevenfold. Nowadays, after corn, soybean is the highest valued crop. The versatile applicability of the crop in different products, oils, and meals has created a high demand throughout the world. In 2020, the U.S. produced 4.42 billion bushels throughout 29 soybean-producing states. In 2019, the total value of U.S. soybean exports to the world gave $18.7 billion.

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An Overview of Soybeans

Soybeans originated in East Asia in China and where featured in the human diet as far back as 5000 BC. Later, in the 19th century, soybeans spread to other parts of the world. The agrotechnical value of soybeans is very high because they leave the soil clean and enriched with nutrients, especially nitrogen.

This crop has many varieties - over 10.000. Their grouping is according to morphological (color and shape of the seed, overgrown fibrous seed) and commercial properties (types for green mass production and combined use).

Deep, loose, and fertile soils with a neutral reaction are preferable as optimal soils.

Over time, soybean production has been greatly advanced. Although we know what the crop needs and how to effectively manage the soil, diseases, and pests can still seriously threaten yields. For soybeans, the most damaging pest to be aware of is soybean cyst nematode."

A Closer Look at SCN

The pest Heterodera glycines (soybean cyst nematode) is a threat to all regions of the world where soybeans are grown. The percentage of yield reduction induced by this nematode can vary from 30-75%. All areas in the U.S. where soybeans are grown are at constant risk.

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Wrather et al. (1997) [1] provided loss estimates for the top 10 soybean-producing countries and concluded that H. glycines worldwide was the most important constraint on yield. Yield losses in 2002 in the U.S. reached $784 million (Wrather et al. (2003)[2].

A plant infested with SCN produces a small number of flowers, smaller grains, and usually dies. Crops on fertile soils with enough moisture develop well, show poorly visible symptoms, and give approximately average yields over one or two years. However, in the following years, the population of nematodes increases, and the plants are strongly chlorinated and poorly developed. The root system of diseased plants is less developed and forms a weaker symbiosis with nitrogen-fixing bacteria, followed by fewer nodes than healthy plants. The most characteristic symptom of the disease is the presence of female nematodes at different stages of development and mature cysts attached to the roots. The optimal temperature for nematode development is 82-88 degrees Fahrenheit.

Soy nematode overwinters as dark brown cysts in the soil at a depth of 90-100 cm. The cysts are leathery and filled with eggs that contain fully developed second-degree larvae. If the temperature (optimum temperature is 75 degrees Fahrenheit) and soil moisture are favorable, the larvae hatch from the eggs and infect the root system. Each female produces 300-600 eggs, most of which remain in her body until extinction. Eggs remain viable in the cyst for up to 11 years. The entire life cycle lasts 21 to 24 days.

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A Review of SCN Management Recommendations

The nematode has a relatively small number of hosts, and its development can easily be prevented by proper crop rotation with non-host crops. Two annual rotations are usually sufficient to significantly reduce its population to a level where it does not pose a threat to obtaining high yields. The application of insecticide is not economically viable, and therefore the use of varieties that are resistant to soy nematodes is recommended.

There are also natural enemies of H.glycines (Paecilomyces lilacinus, P. variotti, and Dactylaria sp.) In nature, this can act as biocontrol agents. In 2003, there was research on these bacterial communities that had positive effects on preventing soy nematode development. [3]

[1] Wrather JA, Anderson TR, Arsyad DM, Gai J, Ploper LD, Porta-Puglia A, Ram HH, Yorinori JT, 1997. Soybean disease loss estimates for the top 10 soybean producing countries in 1994. Plant Disease, 81(1):107-110; 7 ref.

[2] Wrather JA, Koenning SR, Anderson TR, 2003. Effect of diseases on soybean yields in the United States and Ontario (1999 to 2002). Plant Health Progress, March:0-16.

[3] Nour SM, Lawrence JR, Zhu Hong, Swerhone GDW, Welsh M, Welacky TW, Topp E, 2003. Bacteria associated with cysts of the soybean cyst nematode (Heterodera glycines). Applied and Environmental Microbiology, 69(1):607-615.