Profitable Soybean Disease Management in Ohio

Bulletin 895

Nematode Diseases

Many species of nematodes can feed on soybean roots, but only the soybean cyst nematode has been identified as causing substantial yield losses in Ohio. Extreme cases have resulted in a field being removed from soybean production. Soybean cyst nematode is present in all of Ohio's soybean production areas. It is a small microscopic worm that inhabits the soil. The juvenile stages enter soybean or other host roots and begin to feed. Females will establish a feeding site where they reside and produce eggs. The females can be seen in late summer on the roots. The key diagnostic feature for cyst nematode are the white females cysts feeding on soybean roots. Above-ground symptoms of soybean cyst nematode have been limited in Ohio's heavier soils. Occasionally when populations reach very high levels, stunting, uneven plant height, chlorosis, and drastically reduced yields have occurred. Lower populations of cyst nematode (40 to 2,000 eggs per cup of soil) will result in moderate to low yield losses, depending on soil type. Very low populations, less than 40 eggs per cup of soil, rarely cause any loss in yields.

Figure 27. SCN Distribution in Ohio in 2002

Figure 28. Soybeans with very high populations of SCN. Plants are stunted and yellowing.

Soybean cyst nematodes can survive for years in soil and can reproduce on a number of crops and weeds including sweet clover, chick weed, henbit, purple deadnettle, and shepherds purse. Cyst nematode populations are monitored by collecting soil samples and sending them to a laboratory for analysis. The population is measured as the number of eggs or cysts per cup of soil. A healthy female can produce 250 eggs. Depending on soil temperatures, there are at least three generations of soybean cyst in Ohio in any given year.

Figure 29. Resistance to SCN is measured by counting the number of females on a variety to a susceptible check.	Figure 30. Soybean roots with female soybean cyst nematodes, large white pearl-like structures feeding on root.

The best management technique is crop rotation. In one growing season, soybean cyst nematode populations will decline by half when fields are planted with a non-host crop such as corn or wheat. Interestingly, populations may decline by as much as 70% when the field is planted to alfalfa. Figure 31 illustrates changes in SCN populations with different crop rotation schemes.

Figure 31. Changes in SCN Populations with Different Crop Rotation Schemes.

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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-1868