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Corn+Soybean Digest

SCN Signals Can Trick You

Most growers seem to want to find anything but soybean cyst nematode in problem fields.

Maybe that's why it's usually the last thing they look for.

"Farmers will look at pesticides, fertility, soil compaction," says Walker Kirby, University of Illinois plant pathologist. "Soil sampling (for SCN) is usually one of the last things they do."

Maybe that's because SCN is a sneaky little devil, sometimes posing as compaction, herbicide carryover, a nutrient deficiency or any fungal disease imaginable.

"What growers are first seeing is a yellowing of the plants," says John Ferris, a Purdue University nematologist.

That can mean that SCN has a firm hold on those plants - or that the crop has a nutrient deficiency.

SCN is commonly confused with iron chlorosis. But iron chlorosis symptoms usually appear in June; SCN yellowing occurs in July or August.

Some growers hope to cure the yellowing with a shot of manganese, Ferris says. If the crop isn't manganese deficient, however, the beans may look better, but not yield better.

Dry, sandy fields in southern Illinois are often accused of having potash deficiencies rather than SCN. Symptoms of both include a burning or dying of leaf margins, Kirby says.

SCN can be confused with most any fungal-type root disease, Ferris adds.

Some growers may have pockets of phytophthora root rot, rhizoctonia or fusarium root rot, especially if they have heavy soil that stayed wet and cool all spring, warns Pat Donald.

Donald, a University of Missouri extension nematologist, recommends that growers be "good scouts and problem solvers and look at a wide range of things. The best thing a producer can do is dig up a plant and the soil around it and take it to a diagnostic lab to see if there are any diseases."

"Or if they have a thin stand, they can take seed in for a germination test. If they think they have herbicide carryover, they need to go back and look at their records and see what they put on the fields.

"And they can always do a soil test and see if soybean cyst nematodes are present."

Actually, Donald recommends soil testing every soybean field for SCN, whether it appears to have a problem or not.

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