By ANN HINCH
Assistant Editor

URBANA, Ill. — What works to control soybean cyst nematode (SCN) in the South doesn’t have as much effect in the Midwest, according to an Illinois researcher.

At North Carolina State University, plant pathologist Dr. Steve Koenning is finding rotation with corn seems to be the best combatant to soybean yield loss from the tiny SCN roundworm, which was first found in the soil of his state over 50 years ago.
Similar research is being conducted elsewhere, such as the University of Arkansas, and the news is slowly spreading to soybean growers.

“The longer between soybean crops, the better the yield tends to be,” Koenning said.

He noted the anticipated nationwide decrease in soybean planting for 2007 to make way for more corn, recently reported from a USDA survey, may not only be opportune business but also good management of those acres normally dedicated to soybeans routinely afflicted with SCN.

Dr. Terry Niblack, professor of SCN management at the University of Illinois, explained the roundworm probably ended up in the United States courtesy of soil samples from Japan, and that the worm originally evolved alongside soybeans in northern China.
Midwestern soybean farmers have traditionally used rotation and seed resistance against the pest, which attacks plant roots.

In the South, she said soil temperatures remain fairly high through winter months, forcing hatching of the worm’s eggs. Without the nourishment of soybean plants, their numbers decrease; planting another crop such as corn the following spring adds insult to injury, since SCN can’t feed off it.

“Cyst nematodes, in general, have limited host ranges,” Koenning said.

Ridding active fields of them entirely, however, isn’t really an option, since SCN is hardy and some can remain alive through a rotation season to once again feed on soybean roots.

“Nematodes are forever,” he said, adding about the only way to kill the worm is to pave over its host land.

While rotation that skips a year of soybeans may work in southern states such as North Carolina and Arkansas, Niblack said the practice has limited effectiveness the further north one travels.

SCN has adapted better to Midwestern winters, since the colder soil allows the eggs to remain dormant until they can hatch to feed on spring plants.

“They just know how to live in these kinds of conditions,” she said.
“These kinds” of weather conditions are north of Kentucky,
Arkansas and Oklahoma, beginning with Zone 5 of the USDA Plant Hardiness Zones. Zone 6, which is south of 5, includes the aforementioned states and points south, as well as a short distance north into southern Illinois, Indiana, Ohio and Missouri.

The map can be viewed at http:// aggie-horticulture. tamu.edu/wildseed/info/6.1.html online. Niblack said she has not participated in this particular research, but that some has been conducted to show that planting certain grasses over the winter – such as rye grass – and then plowing them into the soil is effective against SCN in the Midwest.