Ag Answers:Scn Symptoms Seen in Northwestern Ohio Fields

Northwestern Ohio fields are showing infestation symptoms of the soybean cyst nematode (SCN), a new pest problem for that region, and one that can cause serious yield losses.

An integrated pest management Extension associate, Curtis Young of Ohio State, says extensive infestations are in Henry, Fulton, Sandusky, Wood and Lucas counties. Farmers in other soybean production areas should also be alert to the possibility of infestation, he says.

The SCN is a microscopic roundworm that feeds on soybean roots. Once predominant only in the South, it has slowly moved into the Midwest in recent years. Ohio State confirmed the state's first SCN case in 1987.

In Indiana, SCN's presence has been confirmed in varying degrees in about 60 of the state's 92 counties, according to Purdue nematologist and SCN researcher, John Ferris. Ferris says SCN is most prevalent in the western two-thirds of the state.

Ferris knows well how formidable SCN can be. "Once you find SCN, you have it forever," he says. "SCN can survive up to five years without soybeans to feed on, so crop rotation alone won't solve the problem. In fact, we don't recommend changing a corn/soybean rotation; we recommend using resistant soybean varieties."

SCN resistance, which is not 100 percent effective, can rid fields of as much as 90 percent of the female nematodes, Ferris says.

The nematode's presence is not apparent until above-ground symptoms are visible on plant tissue. Above-ground symptoms, which may not appear until long after infestation begins, are circular to oval patches of stunted, yellowed plants scattered throughout fields.

Unfortunately, SCN symptoms mimic those of other stresses, such as root injuries, nutrient deficiencies, herbicide injury or soil compaction, OSU's Young says.

"This year, at least in northwestern Ohio, water standing in fields could be the main cause of these symptoms," Young says. "However, when these symptoms are observed on knolls in the field, instead of low spots, they deserve closer examination."

Farmers can examine soybean roots for attached female cyst nematodes. However, the farmer may need a trained professional's help because the pest is smaller than a pinhead. Female cyst nematodes are white to yellow to brown in color, and lemon-shaped. The unaided eye can see them attached to sides of roots, but a magnifying glass is helpful.

Sandy soils are good candidates for infestation, although SCN also is found in heavier soils, Young says. The nematode primarily spreads within and between fields when infested soils become attached to and drop off of farm machinery, especially tillage equipment.

Farmers can confirm SCN's presence by having soils tested by a reputable diagnostic laboratory. Ohio State's C. Wayne Ellett Plant and Pest Diagnostic Clinic, Columbus, performs SCN soil analyses. Purdue's Plant and Pest Diagnostic lab also accepts samples for diagnosis.

Extension offices have sample submission forms and instructions on how to sample fields for SCN. Local Extension agents can provide recommendations for managing SCN problems as well as offering help to reduce the risks of spreading SCN infestations.

Also check OSU Extension Fact Sheet AC-39-96, "Soybean Cyst Nematode," from local Extension offices or on the World Wide Web at: http://www.ag.ohio-state.edu/~ohioline/ac-fact/ac-39.html.