DECATUR, Ill. (DTN) -- Time to head to the field and do a little digging to unearth clues about soybean cyst nematode (SCN) pressure. This time of year, plants may look perfectly healthy above ground, but it is possible to visually spot females feeding on soybean roots.
Soil testing for the presence of SCN is typically done in the fall. However, these in-season spot checks indicate if there is feeding in the field and whether the SCN resistance in the soybean variety planted is working.
SCN females look like small white dots about the size of a grain of sugar -- or about one-tenth the size of the healthy nitrogen-fixing nodules that should be present on soybean roots.
North Dakota State University plant pathologist Sam Markell says it is possible to visually spot females feeding on soybean roots. However, he also likes to take a flashlight and hand lens to the field.
Grab a shovel or a hand trowel and dig the plant and surrounding roots. "Those small, white-colored females are only loosely attached where they feed on the root, so pulling the plant tends to knock them off," said Markell. "Depending on how dry the soil is, I will sometimes take a five-gallon bucket of water to the field and carefully wash the soil off the roots."
Markell says females will swell with 100 to 200 eggs and may go through multiple life cycles, depending on region of the country, before changing to hardened cysts that protect the eggs in the soil. North Dakota may have two to three generations, for example, while Missouri has three to six, he said.
"Each time they go through one of these generations, the levels are increasing in the field," Markell added. "If you are planting a resistant variety and spotting a lot of white females in-season, it likely means that variety is not holding up under SCN pressure very well."
It's also a clue the field needs a serious soil-testing program to identify what levels are present and create a management program using different sources of resistance and/or treatments to start reducing SCN levels to try to control yield loss.
Read a blog post about how SCN and SDS can work together to damage yields here https://www.dtnpf.com/….
For more information on how nematodes hitchhike on soil and move between fields https://www.dtnpf.com/…
Learn more about soybean varietal resistance and how tactics farmers are using https://www.dtnpf.com/…
Find videos and all sorts of SCN management info at www.thescncoalition.com.
Pamela Smith can be reached at firstname.lastname@example.org
Follow her on Twitter @PamSmithDTN
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