Check Soybean Cyst Nematodes in No-Till Fields
By Jan Suszkiw
March 20, 2002
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
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, theres been speculation that no-tills increasing use
has contributed to a rise in SCN populations in Midwestern soybean fields.
However, theres been little actual research investigating this in
Midwestern states, according to nematologist Gregory Noel, at ARS
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 studys 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 isnt an SCN host. Following a 1997
corn planting, for example, the egg count for the plots 1998 harvest fell
to below 12,000 per liter of soil. In 1996, the count was 112,000.
Surprisingly, the pests 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
ARS is the U.S. Department of
Agricultures main scientific research agency.