Corn Helps Check Soybean Cyst Nematodes in No-Till Fields

Farmers who practice no-till, leaving soils unplowed before planting, run little risk of boosting soybean cyst nematode (SCN) populations as long as soybeans are rotated with corn, an Agricultural Research Service study suggests.

Heterodera glycines (SCN), a microscopic roundworm, costs farmers $240 million to $1.5 billion annually in crop losses. During the past decade, one-third of Midwestern farmers have adapted no-till to replenish organic soil matter, curtail erosion and cut production costs.

Recently, there’s been speculation that no-till’s increasing use has contributed to a rise in SCN populations in Midwestern soybean fields. However, there’s been little actual research investigating this in Midwestern states, according to nematologist Gregory Noel, at ARS’ Soybean/Maize Germplasm, Pathology and Genetics Research Unit at Urbana, Ill.

So, in 1994, he initiated a seven-year study on a local field with silty clay loam soils and six percent organic matter to examine what, if any, effect no-till had on SCN populations compared to using conventional tillage, corn-soybean rotations, and SCN-resistant and susceptible cultivars.

Among his observations:

• No-till plots of Williams 82, a susceptible soybean, generally had more nematodes at harvest than conventional tillage plots with the same cultivar. During the study’s third year, no-till plots harbored about 112,000 nematode eggs per liter of soil versus about 64,000 on conventional tillage plots. Both tillage systems, however, yielded 34 bushels per acre.

• Regardless of tillage, yields of the resistant cultivar “Lindford” were 15-34 percent higher than Williams 82. Lindford also had the lowest SCN numbers.

• The sharpest decline in nematode numbers in no-till plots of Williams 82 came after rotations of corn, which isn’t an SCN host. Following a 1997 corn planting, for example, the egg count for the plot’s 1998 harvest fell to below 12,000 per liter of soil. In 1996, the count was 112,000.

Surprisingly, the pest’s 1999-2000 population crashed even further in all research plots. Noel suspects a natural antagonist emerged, such as a parasitic fungus or bacterium, which raises the prospect for a new SCN biocontrol agent.

ARS is the U.S. Department of Agriculture’s main scientific research agency.