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Agronomic Crops Network

Ohio State University Extension


SCN & Soybean Disease Management

These plots were inoculated with soybean cyst nematode (SCN) and other soybean pathogens. Learn more about SCN and soybean diseases below. Questions? Contact Dr. Horacio Lopez-Nicora at

Soybean cyst nematode (SCN)
SCN damages soybeans by feeding on roots, robbing the plants of nutrients, and providing wound sites for root rotting fungi to enter. The severity of symptoms and yield losses are dependent on several factors including: the number of nematodes present in the field at planting, the soybean variety, tillage practices, soil texture, fertility, pH, and environmental conditions during the growing season. In many cases, above-ground symptoms are not present, but yield will be reduced. Once SCN is established in a field, it rarely is eradicated. SCN is the leading cause of soybean yield loss in North America and now occurs in all major soybean production areas worldwide.

Charcoal rot
Charcoal rot of soybeans is most prevalent in the southern and western United States than in the north central region, and on early maturity to mid-maturity group soybeans. The disease is more severe under drought conditions when temperatures are high (28 to 35 °C [82 to 95 °F]). In a recent survey conducted in Ohio, M. phaseolina was detected in over 95% of the soybean fields sampled.

Fusarium seed and root rot is a problem in many fields in Ohio, however, it is difficult to pinpoint as the culprit of yield loss due to its nature as a secondary invader. Cases of Fusarium are most common in fields where plants are predisposed to stress factors such as nutrient deficiency, nematodes, herbicide injury, or other diseases.

Sudden death syndrome (SDS)
Sudden death syndrome (SDS) is caused by the fungus Fusarium virguliforme. Foliar symptoms of SDS are a result of a toxin, produced by the fungus, moving from roots to the leaves. Foliar symptoms rarely appear until after flowering. Leaves of infected plants initially show scattered yellow spots between leaf veins. Spots grow to form large chlorotic and necrotic blotches between the leaf veins, while the midvein and major lateral veins remain green. Leaflets eventually drop, but petioles remain on the stem. Diseased plants have rotted taproots and lateral roots. When stems are cut lengthwise, the woody tissue of the taproot is discolored light gray to brown. This discoloration may extend up to two inches above ground. Bluish fungal growth may be seen on the surface of roots if soil moisture is high. Foliar symptoms of SDS look similar to those of brown stem rot (BSR). A good way to distinguish between BSR and SDS is the presence or absence of internal stem browning. Stems of SDS-infected plants have white pith, while BSR causes brown discoloration of the pith.

Frogeye leaf spot
Frogeye leaf spot is caused by the fungus Cercospora sojina. The disease occurs across the United States and in Ontario, Canada. Frogeye leaf spot can cause significant yield loss when widespread within a field. Leaf lesions are small, irregular to circular in shape, and gray with reddish-brown borders. Most commonly occurring on the upper leaf surface, lesions start as dark, water-soaked spots that vary in size. As lesions age, the central area becomes gray to light brown with dark, red-brown margins. In severe cases, disease can cause premature leaf drop and will spread to stems and pods.