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College of Food, Agricultural, and Environmental Sciences


Variable SCN Counts May Change the Way Farmers Sample Fields

October 14, 2010

WOOSTER, Ohio – It's that time of year to sample fields for soybean cyst nematode, and new Ohio State University research is indicating that soybean producers may need to double up their efforts to analyze soil for eggs.

Ohio Agricultural Research and Development Center plant pathologists have found that the presence of soybean cyst nematode in Ohio fields is highly variable, meaning that one part of a field may not have the pest at all, while another part of the field might be loaded with it.

"We've had growers come to us in the past saying that they know they have SCN in their fields because of the yield loss, but their soil samples tell a different story," said Anne Dorrance, an OARDC plant pathologist. "Now we know what's going on. SCN could be all over the board in a field and a farmer may just not pick up populations when he does the sampling."

The project, funded in part by the North Central Soybean Research Program from check-off dollars, is a three-year, multi-state study evaluating the effects of resistant soybean varieties on SCN populations.

Since 2008, researchers have evaluated the population changes of the pest by counting eggs at planting and after harvest, and determining how well the resistant soybean varieties developed from Hartwig, Peking and PI88788 hold up. The findings are giving researchers insight into how to better manage the pest, which is now found in some capacity in all 88 Ohio counties.

"Hartwig, Peking and PI88788 are the only resistant varieties we have on the market. It takes 20 to 30 years to move the resistant genes into high yielding adapted varieties and get them to the farmer. So these three sources of resistance are all we have in the marketplace right now," said Dorrance, who also holds an Ohio State University Extension appointment. "As a result, it's extremely important that we learn to control SCN by effectively managing these varieties alongside other strategies."

Researchers found that soil type, ag production practices like tillage, and drain tiles can play a role in SCN egg diversity.

"If you have a plot 200 feet long and you sample every 10 feet, one site could have zero eggs and another site could have 3,900 eggs. It's not evenly distributed," said Dorrance.

She recommends that farmers probe the soil close to the root zones of the plants, not in between the rows, to get a more accurate egg count. In addition, farmers are encouraged to sample in multiple, random locations in the field.

"Getting an accurate egg count can mean the different between a successful crop and facing a 50 percent yield loss," said Dorrance.

Specialists recommend soybean producers follow these best management strategies for controlling SCN:

• Zero to 40 eggs – Monitor fields after two crops of soybeans.

• Forty to 200 eggs – Some susceptible varieties may register some yield loss at or above 200 eggs per cup of soil.

• Two hundred to 2,000 eggs – Plant an SCN-resistant variety or rotate to a non-host crop. Some SCN-resistant lines may exhibit yield losses above 2,000 eggs.

• Two thousand to 5,000 eggs – Rotate to a non-host crop next year and return with SCN-resistant soybeans the following year. Dorrance notes that 50 percent to 60 percent yield losses have been recorded in Ohio when susceptible varieties were grown at these populations.

• Five thousand eggs and over – Rotate to a non-host crop for two to three years, then sample the soil to determine populations before planting SCN-resistant varieties.

Dorrance said that growers can also management SCN by rotating from a host to a non-host crop, controlling for sudden death syndrome (the two go hand-in-hand), and managing weeds that can serve as an additional food source. Such crops and weed plants include sweet clover, pea, crown vetch, green beans, wild mustard, purple deadnettle, henbit, pokeweed, and common chickweed.

Candace Pollock
Anne Dorrance